David. My post is correct.
The OP mentions his Vaquero. That makes the gun a New Model. The New Models do not have the recessed chambers like the Old Models. The New models,, such as his Vaquero, the case does headspace on the case mouth,, BUT,,, the rim sticks up above the rear of the cylinder.
Go & measure a New Model .45 convertible. The cylinders will be the same OAL, the same chamber lengths, the same boss length, and the same ratchet length. The rim of the .45 Colt AND the .45 acp both stick up above the rear of the chambers.
So, yes,, you can either ream a NM cylinder to accept the .45 Colt,, OR, you can buy a NM cylinder already cut for .45 Colt. It will work, if the OAL of the cylinder is the same as the current one. Or, if you get one a little longer,, you can hone the boss down to fit the current OAL.
Please do not confuse the OP with mis-information.
My feathers are not ruffled,, but I do have the correct information, and the ability to assist someone about these things.