David,
Ours has a Blissfield that is a piston type, it looks like a cast iron York. I'm not recommending it as a replacement unit this one had a small oil leak from the rear cover that I fixed with a new O-ring about 2 years ago and now I'm seeing a wet spot again, but it does function well the dash air on this one is cold. If the Blissfield goes south I'm going to refit with something like a Sanden.

Did you ever add caster to your Blue Bird?