I am re-powering my 79 Newell. It had a 555 Cummins and I am replacing with a 6V93 Silver with 747HT Allison. My problem is top end RPM differential. The Detroit will not turn up as did the Cummins, so I need to change the gear ratio. I am thinking perhaps a 3:42 or 3:21, but don't like to guess. Anyone with a 6V92 and 4 spd Transmission who could advise me of the ratio in their Newell would be a great help. Thanks Rooster