On the other models: we put a Williams Mike mechanism under a Lobaugh Berkshire. Going the other way is a possibility - and you could sell the 3-rail mechanism for a hundred bucks easy.
But cheaper to buy the Williams Mike outright, then sell the 3-rail Mike. I have a perfect Williams 2-rail Mike that I would sell in a heartbeat for $400, free shipping. Have not yet listed it - grey UP paint.
I think the 3-rail Mike brings $300 and maybe $50 shipping on eBay, so even at my exhorbitant pricing you are out only fifty bucks. Way cheaper than 2-railing.