"Hey fellas, I was wondering if anyone else has thought about replacing a 45ACP cylinder with a 45Long Colt cylinder. on a 1917. Bullet diameter is the same. Anything against it? Why would it not work?"
Yup. If you read old gun magazines from the '50s, this was discussed many times. Starting in the 1970s, I read on this subject many, many times.
Another sticking point in this conversion is the frame lug, which keeps the cylinder from sliding rearward. The one on the 1917 revolvers is thicker than those found on revolvers chambered for rimmed cartridges, due to the extra headspace required for the clipped rounds.
There was an article in an old Gun Digest that featured a dual cylinder 1917. The .45 Colt cylinder for this revolver had a groove turned on the rear of that allowed the use of the 1917 frame lug.
Many .455 S&W revovers were rechambered to .45 Colt. The limitation here is that these cylinders are short. Factory .45 Colt rounds are fine, but handloads using Keith bullets have to be deep seated in order to fit.
A rechambered .455 cylinder with a groove on the rear for the frame lug, fitted to your 1917, seems like your best bet.