I did not realize that the 1955 GMC 100 2nd Series trucks were still six volts.
Chevrolet switched to 12 volts in 1955 2nd Series trucks.
1929 - 1954 Chevrolet Master Parts and Accessories Catalog shows the flywheel below:
Truck Automatic Transmission - Flywheel and Fluid Coupling illustration
I think both GMC & Chevrolet flywheels are the same.
The crankshaft bolts hole pattern probably are different.
They both have 139 teeth.
Welding then machining the gear teeth would be tricky because of the pitch or angle of the teeth.
They have to match the starter gear teeth.
I know the Chevrolet flywheels are hard to come by because they were a one year & three month production in 1954-55 1st series .
GMC production fairs a little better 1953 - 1955 2nd series.
So it should not be as hard to find one.
Call
http://www.restorationhydramatics.com/ talk to Gene in Cali.
Or
http://nwtparts.com/ ask for John.
Or here might be one on
eBay do not know if it is 139 tooth.
This
ONE is 12 volt 168 tooth If you can find the GMC part number that would be helpful?
