There was indeed a P-350, not sure what chassis it was based on though. From the single piston master and the solid axle I would guess you have a vehicle older than the 1970s, maybe from the early 1960s. Some pictures would help. But, the warranty plate would clear any doubts.

As far as transmissions go, you should look into putting a ZF 5 speed in there, it has granny and overdrive and it's a very tough transmission. To do it you'd need some drive shaft work and a hydraulic clutch, but it would be a nice combination.


Sam