If you don't want to use the 6.2 how about trying a 4 or 6bt in the truck. The Multi-fuel LDT motor is too big for the M1010. As stated from bottom of pan to top is about 4 feet in length and yes both the 6BT and the LDT are 6 cylinders, but the LDTs cylinders are much bigger than the 6Bts. If I lay six campbells soup cans in a row and then next to it six 5lbs coffee cans the coffee cans are going to be longer than the soup cans. So the LDT is much longer than the 6BT.
If you could hook a 700r4 up to the LDT I don't think it could take the torque of the big motor. You'de probably go a few yards and blow the trans up.
Small truck smaller motor and trans. Big truck big motor and trans.
Get a M109 duce. It's multi-fueled, standard transmission and you'll have room in the back for the whole family plus the inlaws...