I've read here that Gold Cup slides are narrower than standard Colt slides.  Is it possible to put a standard Gov. Colt slide on a Gold Cup frame?

C'mon, somebody....

They are not narrower through the slide rails, but any slide/frame combo has the possibilty of having fitting issues.   They ARE narrower through the barrel hood, which would mean going to a new barrel, if you have a Gold Cup barrel.  So yes, it's possible, but not a straight forward swap regarding barrels.  What do you have, and what do you intend to do?

If you have a GC, and you want to go to a regular Colt round top slide, then you would also need a new barrel.  If you want to go to a Colt slide strictly to go to fixed sights, you can get an Enhanced slide, which will be just like the GC, but with fixed sights.

Also, Colt slides are expensive.  You can get them from Colt or Brownells.  Unless you're an FFL or get some other trade discount, the price will be fairly high (high enough that I would just go buy a NRM 1991, but that's just me).   Good luck.

Thanks hobbs, you da man!