...Let me add that I once owned an 86 GLH turbo with a lil 195hp 2.2 turbo and that car was a blast. Could beat a V8 mustang{LX or GT} in the standing 1/4 allllll day long....go past 1340 feet and that gap started changin in a hurry. I'll always remember that car....and the dreaded wheel hop it had.
Folks say that youd need a set of forged pistons and a forged crank for a turbo flathead 6...pistons you can get...a crank, not so much! I think it could be done with cast pieces but that's purely speculation on my part due to a lack of anyone having actually done it and lived to tell us about it. The flathead's lack of high reving would be another issue...once again though, finding a purpose built turbo built for low reving would fix that. Installing the proper sized exhaust {1 1/2"?} would keep it breathing well enough, and setting a waste gate correctly would be essencial....the GLH turbo hit 5psi all day long but peaked just at 7psi....5-6psi is enough I think.
I've got a chrysler 265ci 6cyl to play with, so a TBI{s} roughly set for 4 Liters should fit my bill...a smaller motor would require less unless your an overkill kind of person. If I could nail down the TBI{s} and sensors for mine I'd do it in a heartbeat as a bare bones system- crank/ign trigger{HEI dizzy tach sensor lead?}, O2 sensor, amibient air temp or map sensor and I think I'd be good....just haven't put it all together yet.