Howard,
I'm not sure what is going on with the different measurements of these various cartridge heads but I can make an educated guess. I think that when they wrote up those specs they each had a sample or two to measure and as we all know there can be some substancial differences in brass size between different makers. It also makes a difference how they measured their cases and what they used to do the measuring with. You have to be very consistant with your measuring methods to get even close to the same measurements using the same tool over and over. Many of the older calibers may not have been standardised till recently, and with odd calibers you may still find some variations. The .470's should all be the same, though.
Giving the measurements out to four decimal places is just silly, in my opinion. They are just showing off or trying to convince you that they did a better job than the others, it's largely theoretical and means nothing to the average reloader. Measured out to four places, you would be lucky to find one out of a hundred that measured that exact size.
I have found that given three different brands of 45-70 brass, you are apt to find three different sets of measurement figures. Federal makes theirs thickest in the rim thickness, Winchester is somewhat in the middle, and Remington is the thinnest in rim thickness. There is more variation in 45-70 brass than any other caliber that I have checked to date. With it's generally mild pressures, I don't see it as a big problem though, but I do wish they would start making it in a standard size for all manufacturers.
I cut the chambers so that the gun will just close on the thickest rims, but the 45-70 doesn't have the pressure that the .470 does, so my recommendation is that you buy one brand of brass, chamber your gun accordingly, and stick with it throughout your ammo loading.
I really liked your engraving and that print is really nice as well. I think your choice for a big double is spot on, but unless you intend to go to Africa with it, it may be a bit of overkill. I will be watching for further updates and look forward to seeing more pictures of your work and of this project. You said the two donor guns were not as good as you enitially thought. What sort of problems have you encountered with them? Bob