Ruger Older large frame Vaquero in 45 LC add 45 ACP cylinder

I have two Ruger older model Vaqueros (2003 dates) . These are in 45 Colt. Could someone head me in the right direction for adding a 45 ACP cylinder on one of these. So I could have a convertable Vaquero and could fire either cartridge.

Welcome to the Forum!
You can try & buy a spare 45 acp cylinder for a New Model Blackhawk. They will be the same size. BUT,,,,,,,, you need to buy one after you measure the OAL of your current cylinder. Buy the spare at least as long as your current one or a few thousands longer. You can always hone down the boss a few thousands to make it fit. Be prepared to spend around $100-$125 for a spare cylinder.

the new 45ACP cylinder being the same length would keep the head space in check , and the boss keeps the end shake in place, correct??

Correct.
You have to use just the OAL, (from the back of the ratchet to the front of the boss) as your measurement. In general, you rarely need to worry about timing, but I always check any I work on before firing.

Gary Reeder will make one for $250 last time I looked. I had been thinking along the same lines. It would be done correctly, fitted correctly and the correct throats.... Don't care for his bling guns, but this sounds like a fair deal.

well maybe I should just look for a new model blackhawk with the two cylinders and be happy with that.

I have had two non-convertible Ruger Vaqueros that I used 45acp cylinders in.

The first was an old version Vaquero that I purchased a convertible cylinder for. I bought the cylinder from a forum member who checked the overall length, the front portion length, and the ratchet portion length for me before I purchased it. It worked well, but I did have to stone the face of the ratchets just slightly in order to get it to fit and rotate correctly. No problem after that. I seldom used the cylinder, but not because of any problem with the function.

The second was a cylinder from a convertible Blackhawk that I tried in an old version Ruger Birdshead Vaquero. I only shot two cylinders thru it, but the cylinder fit perfectly on the first try, and it shot great. It was a blued cylinder and the Birdshead is polished stainless, so I when I sold the Blackhawk both cylinders went with it.

I bought a cylinder from a member for 50 bucks and installed it in my Bisley myself. Had to stone a smidge off to get it in there but it functions perfectly. The throats were also perfect, which is more than I can say for the original 45 Colt cylinder.

I had to ream the throats on the first cylinder I fitted. Not to hi-jack the thread, but is anyone doing a throat-reamer pass-around or rental at this time? I have another one that needs reaming.

It's a fairly easy conversion with the hardest obstacle finding a donor cylinder.
I currently have a extra should you be interested.

nice looking revolver you have there. Sent a PM