LonnieC
The 12v replacement motor I used was a unimotor. I didnt remember that untill you posted your pics.
I purchased mine through Truckshop in orange a few years ago, it is a unimotor
14522 I see it offered on ebay item number 200422546935
That motor fits inside the old 6v
housing I used some pieces of rubber as
spacers I had to file the new housing a little on the back, you can see that in the pic.
I dont remember the shaft diameter, I could have used a 1/4 to 5/16 shaft bushing, you can get those at the hardware store.
Again this was on a 50 and a Harrison H-02-47 (May not help you guys with a 54)
Good Luck