I've been following this but didn't comment till now. If you need more power in your 7500 6X6, you may just want to bump up to a 478. I drove a '62 6500 with a 478 and it had no problem pulling 35,000, even up hill. Might not have been the fastest, but it sure had power.
Side note: How high to rev it and when to shift/downshift played a pretty big part in producing the power of it. (You don't need to max out the revs like you would a Detroit).
Bill
