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Where do you plan on buying whatever rotor you need? Don't bother going to a Ford dealer, because both are obsolete.
I found (1) D6TZ-1102-E (at a Ford dealer in KS) & (45) E1TZ-1102-B NOS. Most of these are located at obsolete parts vendors.
The closest source to MS for E1TZ-1102-B = CARPENTER NOS OBSOLETE PARTS in Concord NC has 39 = 800-476-9653.
Try an auto parts store, should be cheaper than NOS
I'd contact and ask the part vendor like Dennis Carpenter is the are spec sheets on the rotors and see if there are stated thickness difference between them part # wise.
There are two possible hub & rotor assy's for the OP's 1978 F250 4WD w/Dana 44 w/3,800 lbs. capacity:
D6TZ-1102-E or E1TZ-1102-B (replaced D7TZ-1102-A & E0TZ-1102-G).
Differences: Without free running hubs (E1TZ-1102-B), or with free running hubs (D6TZ-1102-E).