Internals...

Do all the turbo motors use the old castings, or is my motor not original to the car? The motor I got out of an '89 XR4Ti has a pretty much all '74 castings in it (rods, oil pump, crank, etc.) Is this because the motor was originally built for industrial purposes???
 
You're probably referring to the D4 part number cast on the block and rods. That doesn't mean the block is '74 vintage, it just means there's been no major changes since '74 to that particular casting. The original rods in my '91 block have the D4 series part number. I guess if it wasn't broke, they wasn't fixin it. :)

There's a date stamping somewhere on the block, but I don't know where and don't know how it breaks down. That will tell you the actual date the casting was made.
 
the block casting should be a E1 or E3
D4 is a deff a NA block
I just looked at 4 Turbo blocks all of them are E3ZE

D4 on the rods is fine, the crank is about the same till they went to the small main with the DP engine
even the 2 piece rear main seal style crank will go into a one piece rear main style block, all ford did ther was grind off the oil slinger

the easyest way to tell if ya have a turbo block is to look ok the pass side right behind where the mount bolts in and see if ya have the oil return hole for the turbo there, if ya do its a turbo block , if not its NA block and the turbo oil return is mounted to the oil pan