I got an 81B mech from a customer who owns a retro gaming shop in Houston.
He wanted his coin mech to work on tokens that he would sell for a dollar.
I switched out the nickel/dime rejector for a quarter rejector...made a few modifications and it works like a champ. Pennines, nickels and dimes fall straight through to the coin return cup, quarters get stuck and are scavenged out by the crank and tokens go straight into the mech.
Something to think about if you want to use your machine to make money!
Same modification would work on any SD mech - ie. V-39, V-81 A or B, C-51 as long as a quarter fit into the coin bezel - they do on a cast bezel, but not sure about the stamped bezel.