Wow Billy3744, You had to really go into the deep dark depths of this forum to find this one.
Basicly all the Revell 598 and 608/616 class FBM kits were just outlines of what info was availible back then on these boats. If you want to do a desk model then these look okay closed up and painted black. But for inside detail I can't think of a kit that is accurate. The props are all wrong as is the shape of the missledeck where it meets the forward Hull. ( the 598 class boats were Skipjack Class Attack boats cut in half and a Missle section inserted) One reason why these boomers were faster than Threasher/Permit class Attack boats.. The 608s were the USAs first "True FBMs " and the 616 and 640 class Boomers were all very similar in appearence with minor differences in their outline.
If you are a hard core Submarine modeller like I am then I found the best way to go is a company called Yankee Modelworks. They do 1/350 scale resin models of most US and Soviet Classes of boats. And for the most part are excellent models. They also do American Fleet Boats and German type VIIs and WW1 Boots. Dragon also does excellent kits of the 688 and Ohio class boats as well as some Soviet boats.
The Resin kits are expensive but well worth it.
The King of The Hill is Revell's new Typ VIIc UBoot in 1/72 scale..
Oh I forgot the Revell Fleet Boat is OK and their Skipjack model can be saved.
I hope this is helpful. Hey if you have the old Revell FBM kit build it anyway.
Most people would not know the difference and it "Looks like a Boomer".
Good Luck