Fe vs FT seems to cause a lot of discussion everywhere, so here's my input:

The blocks are the same with one small but important variation; the hole in the block where the distributor shaft goes is of a different inside diameter, with the light duty and passenger cars being smaller, So, the truck distributor will not fit into the FE block. The light duty distrbutors will fit into the FT blocks but not have the side support needed and will cause the distributor gear to wear rapidly.
Also, the oil pump key/driveshaft is a larger hex on the FTs and require the larger FT oil pump.

The crankshafts, both iron and steel, are the same with the exception of the snout being of a larger diameter and if the crank is to be used in an FE the snout diameter must be reduced to the same dismeter as the FE's and a new keyway cut. The FTs are internally balanced to a lower rpm and must be rebalanced for higher rpm usage.

The rest is nearly all interchangable. The heads of most FTs and industrial engines have a dual manifold heat passage, small intake ports and valve rotators on the smallish valves. The pistons will usually have a dish or reduced piston pin to piston crown measurement to reduce compression.

Hopefully this is about all of the major differences. I'm sure that if I forgot something it will be cleared up by others here.