When we put 3lm on ours, we had to grid/ cut to fit. Had the same exact problem you have. Was literally just taking little off at a time till was able to put boot on. That 1/4-3/8 number sounds correct. Hope this is helpful.
Will have to change front hub and damper from truck engine to the one from the 4386. They are different and truck one will not work with the front mount hydraulic pump bracket.
If the truck one has the coolant filter as part of the cooler, the frame is in the way of the filter. I don’t remember if it is just a little or a bunch. Hope this helps.