Yes this is confusing.
He has a Vaquero which is a NM gun.
You sold him a;
OM frame frame, it can be accomplished but takes some work, mostly removing material for the NM Trigger Spring to work,,,
And it will need a hole drilled thru the frame to hold the Trigger Spring AND a hole to hold the cross pin to hold the legs of the trigger spring, and it will need a hole for the Cylinder Latch Spring & Plunger. All of this work takes some skill & capacity,,,, easy for some, impossible for others.
NM frame to a OM, is a bit easier only needing a OM Spring Block added,,,
OR a empty 22 case JB Welded, in lieu of the Spring Block.
I see you were providing clarification, When it comes to Brass Grip Frame, IMO it's worth doing the extra to get it to work.
However Mr DeerStalker has a NM frame for sale in the classifieds.
And I would be interested in the OM Brass Birdshead if that helps any. I was thinking about buying Deerstalkers but have a NM XR3-RED that I can cut to Birds head.
Here is pictures of that frame showing the extra holes needed and the material that needs to be removed for the Trigger Spring