When putting an extra slide on an existing gun: IF the gun is a good shooter, only fit the new slide and don't touch the frame! IF the gun shoots so-so, you may as well have everything done at the same time!
The last 1911 I put together was around 1994 or 5. On my personal gun with a light weight frame, it cracked at the dust cover at around 800 rounds (kind of normal for Federal Ordinance frames!) I bought a brand new Essex blued steel frame. The slide was a very little bit more loose (probably from fitting the other frame) than I like. I like my field (now called "Carry") guns to be a little lose but not rattle! To bring it back to my specs, I pad the jaws on a 4 or 6 inch bench vise, and give the whole slide a slight squeeze, repeat as needed. After the tune up, I gave it the standard mud bath and check for function when full of mud and grime. With my reloaded Ball spec ammo, it will do 4" at 25 yards, my normal spec is 8" at 25 yards. Clean it up. My guns were guaranteed to feed, function, and go bang every shot. My personal 1911 will function not only full of mud, but full of sand! (Found that out the hard way on a 3 day canoe trip!)
Ivan