It really depends on what you're trying to do.
The Revell Mayflower is a scale model - a remarkably good one - of the Mayflower II, the modern replica that crossed the Atlantic in 1957 and is still on public exhibition at Plymouth, Massachusetts. She was designed by William A. Baker, longtime Professor of Naval Architecture at the Massachusetts Institute of Technology and one of the most respected experts on seventeenth-century shipbuilding of his time - or since. The replica vessel, so far as I know, is still regarded as a fine exercise in scholarship. Mr. Baker did make one substantial concession to practicality: he gave the ship about a foot of extra headroom between decks, for the convenience of modern tourists. Otherwise the ship is, I think, pretty generally regarded as a reasonable interpretation of what the real Mayflower probably looked like.
There have been two modern reconstructions of the Susan Constant. The first was built for the 1957 celebration of the 350th anniversary of the founding of Jamestown. It was designed by a Virginia enthusiast named Robert Fee, with considerable help from a mural that the marine artist Griffin Bailey Coale had painted on one of the walls of the Virginia State House several years earlier. (The state legislature stipulated that Fee's design had to match the painting.) Shortly after that replica was launched it came under some pretty severe criticism from a number of experts - including, most notably, Mr. Baker. It was never taken seriously by historic ship enthusiasts. It rotted to pieces sometime in the late seventies or early eighties.
The state then commissioned a replacement Susan Constant, and hired the well-known British expert Brian Lavery to draw the plans. This time they did it right. Mr. Lavery did a great deal of research on early-seventeenth-century merchant ships, and the ship he designed, though she doesn't look much like Mr. Coale's painting, is widely regarded as one of the best replica vessels around. (Just don't lift the lid on the box-like structure at the break of the quarterdeck. That's where the throttle lever and other controls for the diesel engine are located.)
I haven't been on board the Mayflower II for about 35 years, but I'm pretty familiar with the Susan Constant. My students and I take a field trip to Jamestown Settlement State Park every November, and spend a fair amount of time on board her - and the replicas of the smaller Godspeed and Discovery. A new replica of the Godspeed (the third) is currently under construction. Recent research has established that the real ship was a little larger than the present replica - and the park is expecting a huge increase in visitation for the 400th anniversary in 2007.
The most important thing for a modeler to remember about these replica vessels is that, though the scholarship that produced them is excellent, the researchers had to rely on a tiny amount of actual evidence. As I recall, two facts about the Mayflower are known: she was of 180 tons burthen and her rig included at least one topsail. (One of the Pilgrim journals contains a reference to somebody falling overboard and saving himself by grabbing a topsail halyard that was trailing in the water.) All we know about the Susan Constant is that, according to the records of the Virginia Company, she was of 120 tons burthen. That's it. Everything other feature of any replica of either ship, full-size or model, is based on inference and speculation.
The Mayflower II and the replica Susan Constant look quite a bit different - as the original ships probably did. But since both replicas are highly speculative, and the two original ships were just about the same size, I suppose if a modeler put the label Susan Constant on a model built from the Revell Mayflower kit (and scraped the carved flower off the transom) nobody could prove the model was wrong. (The Mayflower was noticeably larger, but the available information is so vague that oen could probably deal with that problem by saying the Susan Constant model is on a slightly larger scale. I think the smaller Revell kit is on about 1/110 scale; if you said your model was on 1/96, it would be about the size of the Susan Constant. Come to think of it, that would also solve the problem of the extra headroom between decks.) The biggest problem probably would be that students and enthusiasts of American maritime history can recognize the shape of the Mayflower II from a mile away; such people would immediately realize what the modeler had done. But most people probably wouldn't know the difference.
Fortunately there are a couple of good sources on these two subjects. Mr. Baker's The Mayflower and Other Colonial Vessels contains a set of plans, drawn with modelers in mind, for the Mayflower II. (I strongly recommend those plans - especially the rigging diagram - to anybody undertaking the Revell kit.) And Mr. Lavery has written The Colonial Merchantman Susan Constant, 1605, for the Conway Maritime Press's Anatomy of the Ship series.
The replica vessels also have good websites. For the Mayflower II:
For the Susan Constant:
Hope that helps a little.