Brent - I would say, yes.
Some of the rifles shown probably date as late as the 1790s. But more imporatantly, the dimensions are very helpful when building - even a bit later longrifle - as it helps you know you are within reasonable bounds on the proportions of various areas.
If I were starting from scratch getting references together for building a first longrifle of the pre-1800 period I would start with RCA, and then one of most basic books out there with regard to building instruction. For me, these are the Chuck Dixon book (which I think sells for about $25) or Jim Johnston's "Building the Kentucky Rifle" (sells for $10). These books have good drawings and do a complete job of showing the basic layout, techniques and order of assembly. Especially if you are building from a kit or precarve, it's helpful for a first time builder to keep it simple and have brief text with a clear progression of steps emphasizing the fundamentals. Beyond that - you get into decoration, finishes, customizing, and a lot of information on these steps can be found here in the archives or ask various builders - most are happy to help you out.
Guy