There are some "parts kits" for 1911.
Most reasonably decent.
But, they will all require at least some fitting. Which will require some careful filing of working parts, which can be complicated, like the swinging link--it must remain concentric--some minor, like the side-to-side fit of the grip safety.
Now, just from my memory, I've never seen a parts kit in a long slide version. Not entirely sure I've ever seen a 7 inch. (IIRC, AMT's stainless Longslide was 6").
To get a 7 inch barrel, you either need to graft on about 2" of slide, or just let 2" of the barrel poke out the barrel bushing. That latter is probably the one with the least needs for both welding and machining. However, I'm not sure that there are 7 inch barrels to "drop in" (e.g. buy, then file until fit). Cor-Bon might have some, though.
I built a Caspian once, but only the once. Sold it for what I had in it, too. Would I do it again? Probably not, even if the Sarco and Patriot kits look ok, I can buy ready-to shoot for a lot less effort. And, unlike an 80% Glock, a n 80% 1911 is a ton of work.