Conch1, You bring up an interesting question. As a semi auto, since it would be a home build, the number shouldn't matter, even if it matches one in the NFA. They will not show as the same model. If one were building on a registered plate, that would have a number already. Mine is numbered to match my trunnion number. If you follow that rule, you should be totally safe.
The transferable 1928s, most of which were build in 1917A1 style, were largely made on existing M37 registered plates that were extensively reworked. That's why they say "Model 37", and they are papered as M37s since that's what the rules required. The fellow who did that work is also the engraver I used. I spent some time tracking him down, and the two designs pictured/linked on this thread are his handiwork.
That brings up a question, raised by sidewinder above. I have great respect for Orion and know the quality of the work he does. However, I also have to respect the proprietary work of the fellow referred to above. I can't stop anyone from copying from the images, and these designs were published elsewhere long before it was done here. But I can't go out of my way to aid that. It's an ethical issue for me. Now, if anyone wants the name of the engraver who originally did these designs and who I used, e-mail or PM me and I'll give his name and contact info privately. He is very good, but you do pay for his talent.