The 345 is backed by the IH727. The case is unique to IH but the guts are more or less the same as any other 727.
a 360 is a good choice, but you will need to find a matching tranny. If your current IH727 is fresh you might be able to save a couple of bucks by swapping the guts. You could also swap the tailhousing and keep the D20. You will need to fab all new mounts.
The 345:
weighs about 750 lbs
probably produces <100 HP (assuming your block is 28 years old, hell it only had 160 from the factory)
will run forever 300K+.
Nearly free if you come get the one off my shop floor
The 345 is not:
A torque monster, stump puller or the like
a good power to weight ratio
a good rockcrawling motor
cheap to build
as for me I am adding over 100 cubes and losing over 100 pounds...