You didn't create a stir,, at all. Quite the contrary,, you got your answers,, !
hittman only did something I've been guilty of as well,,, mis-reading a post. We are all good!
He IS correct in the fact that in the OM 45's,, there were fewer of those built than the OM .44 Ft handguns. Those OM 45's do enjoy a premium,, and especially those that are convertible or that were shipped with a grass g/f. THOSE need a letter to confirm their "as shipped" condition.
On your NM,, yes,, it sure does look like it likes the ACP cylinder. You do need to find a NM Colt cylinder to match.
You now know what to look for,, (the length of the cylinder boss,) but one thing not mentioned was to take your ACP cylinder,, measure the OAL. Buy a Colt cylinder the same length or a few thousands longer. You can then hone down the boss to fit yours if necessary.
Luckily,, the way those were built,, the timing of the cylinder isn't often (almost never) an issue.
Go on a hunt for a NM 45 Colt cylinder. Expect to pay $125-$150 for one.