A couple of years ago I looked at a late 40's Diamond T 201 pickup with the original CBQXLD Hercules engine that the guy had put a turbocharger on.  He said it ran fine and had more power.  Have talked to others who indicate this kind of Hercules engine is a low-revving machine that will eventually self-destruct if pushed too hard.  I personally would not do it, but maybe the crawler engines are different.