I have a chance to buy a vaquero birds head in 45acp at a great price and am wondering if it can be converted to 45lc as well. I see lots of places that say you can go from 45lc to 45 app but know the other way. I know someone will have an answer here.
Sounds like you want to ream the existing cylinder to LC .
Just find a second LC cyl . Cheaper and you end up with convertible.
Takes a little looking but they do show up.
Unless,,,, by new model you mean midframe. That might be harder
Ruger did no one any favors when they named the 'second generation', mid-sized frame guns the "New Vaquero". All Vaqueros are "New Models" having been designed and built with the lockwork which includes the transfer bar. If yours is actually stamped "New Vaquero" it has a smaller frame and takes a smaller and shorter cylinder than the New Model Blackhawk frame.
Since that pistol was sold as a convertible, Ruger would probably fit a new cylinder for you. I think it might be cheaper to do it that way than pay a gunsmith to rebore six holes and adapt the ACP cylinder. Worth a phone call, anyway.