Drop in parts
As a couple of experienced and respected members have said, there are no drop in parts on a properly fitted 1911A1.
However, meaning no disrespect to people with years of gunsmithing the 1911, the Army did it differently. My experience is from the 1970s, and only with service grade guns, but all replacement parts we installed were "drop in", and were not "touched up" any. If the gun still wouldn't function correctly with the replacement part, the replacement part was replaced, until it worked.
Small Arms repairmen were taught (only) replacement of parts. Many of us learned a great deal more, but many also did not. The guns did work when they left the shop, but that's all we were responsible for. Somehow, I don't think you want this level of performance from your 1911.