This is what I've got so far Eric
I'll need to take a trip to my public storage unit … I have a box of stuff I removed from my Pantera. Plus I have a 4300D on the shelf. Once I see what all is in there I should be able to document the EGR vacuum controls, fingers crossed.
Might take a couple of days, today is booked.
By the way there is a drawing of a 1974 emissions system (I'm sure its the same as 1973) in the parts book, section 90 illustration 3. Hard to follow. I'm sure you'd prefer a schematic like above.