Dear Bert;
The orginal 10" diaphram (truck) assembly will be just fine. We used these all through the 50s & 60s (drags) W/O any problems if It's ballanced.
Ther's a little (give) there, but that's okay.
Those that used the Hayes (spring type) with NO give, snapped axles all the time.
Surface the face with a DA sander or have it done at a Machine Shop and your "good to go"....
Remember; That unit was made for the series 40 truck which hauled 5,000# loads & more.
Good luck.
