I have a 727 from a motorhome, instead of a sliding spline yoke, it has a fixed yoke. Should be easy to adapt over to what the Mack has. What do you mean by not as heavy duty? Every 440 before 1973 was a steel crank engine, just like the 413. The 440 cast crank is still pretty substantial, about triple what a small block chevy has lol. The early 413's did have an odd 8 bolt thick crank setup, but the later ones were the same as a 440. The odd thickness and 8 bolt setup on the early 413's were due to them being hooked to the early cast iron automtic transmisisons. Id love to swap a 12v cummins in, but everybody who has one thinks it is gold plated. One day I will find a deal on a 12v or some other diesel to swap in. I have alot of other projects going on at home already lol, right now I just want to make it semi-drivable. I had a dodge D-800 with a 413 in it and a spicer 5 spd. It also had a large rear axle like this, and It would move pretty good with the 413. I might just leave it all stock for now and use the 401, because I would have to rig up an air pump for the air brakes if I dropped the 440 in... etc