You seem a little vague on when was the last time you had any contact with the guy, from what you said, it seems like at least 2 years? IMHO that is a long time to be out of contact with someone holding thousands of dollars of your machinery and consider a friend. Also not having anything in writing was a big mistake, what if at any time the guy passed away, how would his heirs know those machines were yours, or care? I'm not saying its you fault, the guy absolutely should have contacted you and given you a chance to get you machines back, but I think you might want to share some of the responsibility for things going awry.
I also agree with the other comments here that it is imperative you speak directly with the guy, I'd even reach out to the guy who bought the shop and at least let him know whats going on. Stewing in anger and plotting revenge is not going to resolve the issue, it will likely just bring more frustration an harm upon you.