I am reading what others are saying however my own personal experiences counter what others are saying. If you look closely at the Main Drive Gear (a/k/a Input Shaft) you will see two holes 180° apart in the bottom of the gear area. These are there to lubricate the Main Drive Gear Bearing. How this works is the Intermediate Gear meshes with the Main Drive gear and forces lube (picked up by the 2nd gear) into those holes. When the transmission is in High Gear, the Main Drive Gear is engaged into the Cluster and they spin simultaneously where there is no need for that Main Drive bearing to be lubed, however, when only the Main Shaft is turning (from the driveshaft), there is nothing to provide lubrication for that bearing. I have personally seen several instances where that bearing seized itself to the Main Shaft simply because the bearing ran dry. So how long will it go?? That I do not have an answer for you, so guess it is how much you want to gamble on it.
As for flat towing hubs, if I had to have them, I would make them. The Carnegie boys have done something similar and towed their Model-Ts with them with success. I would fabricate a flat plate with a 5 on 5½ inch hole pattern and mount a tow dolly hub to the plate. Then use a 15" wheel to still have fenderclearance. Just mount the adapter and set the Model-A emergency brake to keep the adapter from rotating. Rough sketch below...
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