I haven't looked at the grand old Revell kit up-close for many years, but I'm sure Shipwreck's description is accurate.
If those pinrails are to bear the strain of shrouds and running rigging set up to scale, some degree of compromise probably is just about inevitable. My guess is that if the chainplates for the shrouds and backstays were made of wire running down through the waterways, the deviation from reality would be almost invisible. When the model's finished, most of those belaying pins will have coils of line hanging from them; it would take a real eagle eye to peer under the pinrail and between the coils in order to see that the chainplates (a) aren't shaped quite right, and (b) terminate in the waterways rather than being riveted to the bulwark plating. I suppose it would be possible to reproduce the rivet arrangement pretty accurately, and thereby pin the ends of the chainplates to the bulwarks, but I don't know how many observers of the finished model would be able to see such a detail. But narrowing the pinrails, getting rid of those awful plastic bars on the bottoms of the deadeyes, and rigging the deadeyes with genuine lanyards would make a big difference to the look of the finished model.
I should emphasize, though, that I haven't tried it and I don't have the kit in front of me. All these suggestions are coming out of my head, on the basis of the Campbell plans and highly unreliable memory of the kit.
I strongly recommend replacing the plastic belaying pins in any case. I'm a big fan of plastic sailing ship kits, but we need to acknowledge that certain components of a real ship just don't lend themselves to reproduction in styrene. Belaying pins are a prime example. Even if they haven't been busted off before you open the box (as they may well have been), they just aren't strong enough to do the job. The extra effort and expense of replacing them will be amply rewarded when you reach the running rigging. And once you've sliced off the plastic ones, and sanded the top of the pinrail smooth, it's just as easy to drill the holes for the replacements in the right places as the wrong ones.
Even if the plastic belaying pins aren't replaced, there's a problem regarding the strength of the pinrails. I built several Cutty Sarks and a couple of Thermopyaes when I was much younger, and I remember the sick feeling when, midway through the running rigging process, several of the pinrails simply busted loose from the bulwarks. Wire chainplates would go some way toward solving the problem, by taking the strain of the shrouds off the pinrails and transferring that strain to the waterways (or the bulwarks). Another trick, which I've used on several models (including the little scratchbuilt frigate Hancock that's shown in my avatar) is to reinforce the joint where the pinrail joins the bulwark. In the case of that particular model I used L-shaped ABS "girders" from Plastruct. Each pinrail has a Plastruct girder, slightly shorter than the pinrail itself, underneath; the girder is completely concealed on the finished model. On a model as big as the 1/96 Cutty Sark, a small strip of basswood will work just as well. But I'd strongly recommend doing something to beef up the pinrails - at least the wide ones in way of the shrouds and backstays. When you reach the running rigging stage, you'll find your life is considerably simpler if you know you don't need to worry about a pinrail coming loose.
Rigging a Revell Cutty Sark completely with aftermarked blocks and deadeyes probably would cost at least a couple of hundred dollars, and I certainly don't blame anybody who declines to spend his money that way. I have, however, noticed something odd about this in other threads. When newcomers decide to buy aftermarket parts like that, they seem, for some reason, to think they have to order the complete outfit for the ship at once. (I remember one case, in another thread, of a modeler who spent several hundred dollars, sight unseen, on blocks and deadeyes for a Heller Victory before he finished painting the hull - and then found out a lot of the parts he'd bought were in the wrong sizes.) That just doesn't make sense.
If you're confronting the prospect of replacing the deadeyes of the Revell Cutty Sark, and you haven't started the model yet, the only deadeyes you need to worry about now are the lower ones in the pairs for the lower shrouds and the backstays. By my count (based on Mr. Campbell's drawings) there are 68 of them, in four sizes. (In practical terms the difference between a 6" deadeye and a 7" one probably isn't worth worrying about on this scale. You probably can do a nice job with two sizes - 3/32" and 1/8".) Bluejacket britannia metal deadeyes ("lower, scored, unstropped"), in those sizes (which are a little big, but probably not intolerably so), cost $2.25 and $2.35 per dozen, respectively. So we're talking about an initial purchase of six dozen, costing (including shipping) about $20.00. If you work at the rate I do (which isn't saying much; maybe you work quite a bit faster), you won't need any more deadeyes for several months. Then you'll need another three dozen ("upper, scored, unstropped") to set up the lower shrouds. (No need to worry about the backstay deadeyes till you've set up the topmasts.)
My personal habit when I'm working on a ship model's rigging is to order as many blocks and deadeyes as I figure I'll need in a month or so. When I notice the supply is getting low, I order another month's worth. To me, that makes sense - and the modest family budget can handle those incremental expenses of $10.00 to $20.00 per month without creating a financial crisis. (My wife used to balk at my insistence that the kids could go without food one or two days per month, but they're out of the house now. If one of my Bluejacket orders means one of the cars has to go without gas for a few days, so she has to walk the ten miles to work - well, it's good for her. Just kidding, Anne.)
Again, I'm not trying to drum up business for Bluejacket, and I certainly don't want to imply that it's "necessary" to buy aftermarket parts for a model like this. But I do think it's worth thinking about model building as an investment in leisure-time activity. Even with those aftermarket parts thrown in, it's lots cheaper than most. It is, in fact, one of the cheaper hobbies a person can choose.