Those pictures of the Off-highway Macks sure bring back some memories!
The company had a wide range of those at various quarries in a few states back in the day. Everything from the little M-15's which were built with rear axles similar to what they used in the DM-800 five speed Maxi-Torque transmissions and I believe ENDT-865 V-8 engines. Then we had 3 or 4 M-30's with NT-855 Cummins and CLBT 56400 Allisons. Then Some M-35 with KT1150 Cummins and CLBT 5860 Allisons. Then a couple M-50's with 16V-71 and I believe thos had the CLBT-6061 Allisons. And the biggest in New York State were the M-65's with the 8000 series Allisons.
May have missed one or two in there, or got engine models and transmission models a bit off, been a few years!
I do recall there was one truck that had a Allison 750 series transmission we figured that was built to the price point for someone as I believe it was mated to a KT-1150 rated at the same horse power as the maximum that transmission was rated to handle!
Those M-30 were "fun ones" to work on as they had direct mount transmissions, real fun when it came time to pull the transmission. The trick we came up with to lower them was first roll the windows down on the cab doors. Then slide a good solid railroad tie through the doors. Fabricate a lifting bracket to the top of transmission. Put jack under rear of engine. Hook chain jack between the railroad tie and lifting bracket to hold weight while unbolting the mounting plates that went from rear of transmission to rear of engine on each side. Remove the hand hole cover on front side of flywheel housing at the bottom and remove one flex plate bolt at a time, turn to get access to next bolt and repeat till all 12 bolts were out. Then proceed to remove something like 21 7/16 bolts that held the transmission to the flywheel. Almost forgot, have to remove shift linkage, top mount PTO and rear drive shaft!
Now the fun work starts, hook another chain jack to the rear yoke of transmission and the rear axle. Then have a small guy who could fit through the window holes in the door crawl in the cab to work one chain jack to support the transmission while another guy works the other chain jack to pull the transmission back while the guy in cab slowly lowers the transmission to the ground being careful to not let the ring gear teeth, yes ring gear is part of the transmission, not gouge up the gasket surface of the flywheel housing.
Almost more fun going in because you have to be even more careful of the transmission to flywheel housing gasket or you might have to do all this a second time!