according to the FAQ posted at the top of the CUCV forum it says:
Belts ( all but M1010 )
- Driver side alt- Gates# 7575; Dayco# 15580
- Passenger side alt- Gates# 7483; Dayco# 15490
- Power Steering- Gates# 7448; Dayco#15455
When installing Gatorbacks, I (LavaRok) choose the following three belts:
- Driver side alt - 15585 ( 58 )
- Power steering - 15461 ( 45.5 )
- Passenger side alt - 15491 ( 48.5 )
However, the P side alt was tight. I'd try the 15495 ( 49 ) next time.
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hope that helps, it also never hurts to take the old belts in, or if they are still on the truck to have them step outside and look, no shame in having them measure or compare