Usually when people do this they cut the bellhousing in half and weld it to the front half of the B18/20 belhousing so the gearbox sits upright. Certainly on the M47 lubrication was marginal anyway and I wouldn't be surprised if it was being lubricated properly when sitting permanetly on the piss (technical term).

However that won't cause overheating of the other components; have you checked the driveshaft is short enough? If it is compressed all the way when initially fitted the suspension can't move in one direction and I imagine the resultant compression force on the pinion and twisting on the centre bearing would generate impressive amounts of heat.

Regards

Pete