Sorry to be such a dumba$$, but when you speak of the "trap door", are you talking about the dust cover, or is this some new sort of upper? I'm seriously contemplating building my first complete upper, and inquiring minds want to know. Thanks!
Lots of good suggestions above. You might also check out the offerings from Smith & Wesson and Dan Wesson. With 1911s it just depends on what you want and how much cash you are willing to drop. Good luck. They are addicting!