Yes, its a waste of time to make these sub-variants.
As far as I know, the 7Q and 70A are very similar internally (maybe identical?).
The best thing about it was the long cowl, which made it look better than the standard JT9.
The -70A’s do have a RR vibe to them I think.
Here’s a list of NW 747 classics back in the day. (1998)
Active :
747-151 -- L/N 027, S/N 19778, JT9D-7A
747-151 -- L/N 045, S/N 19780, JT9D-7A
747-151 -- L/N 075, S/N 19785, JT9D-7A
747-251B, L/N 088, S/N 20356, JT9D-7F
747-251B, L/N 135, S/N 20357, JT9D-7F
747-251B, L/N 141, S/N 20358, JT9D-7F
747-251B, L/N 163, S/N 20359, JT9D-7F
747-251B, L/N 165, S/N 20360, JT9D-7Q
747-251F, L/N 258, S/N 21120, JT9D-7F
747-251F, L/N 261, S/N 21121, JT9D-7F
747-251F, L/N 269, S/N 21122, JT9D-7F
747-251F, L/N 308, S/N 21321, JT9D-7F
747-251B, L/N 357, S/N 21704, JT9D-7Q
747-251B, L/N 374, S/N 21705, JT9D-7Q
747-251B, L/N 377, S/N 21706, JT9D-7Q
747-251B, L/N 378, S/N 21707, JT9D-7Q
747-251B, L/N 379, S/N 21708, JT9D-7Q
747-2J9F, L/N 400, S/N 21668, JT9D-7F
747-251B, L/N 412, S/N 21709, JT9D-7Q
747-251B, L/N 442, S/N 22389, JT9D-7Q
747-251F, L/N 444, S/N 22388, JT9D-7F
747-251B, L/N 594, S/N 23111, JT9D-7R4G2
747-251B, L/N 595, S/N 23112, JT9D-7R4G2
747-251B, L/N 642, S/N 23547, JT9D-7R4G2
747-251B, L/N 644, S/N 23548, JT9D-7R4G2
747-251B, L/N 651, S/N 23549, JT9D-7R4G2
747-251F, L/N 680, S/N 23887, JT9D-7Q
747-251F, L/N 682, S/N 23888, JT9D-7Q
747-227B, L/N 375, S/N 21682, JT9D-7Q
747-227B, L/N 437, S/N 21991, JT9D-7Q
747-227B, L/N 465, S/N 22234, JT9D-7Q
747-212B, L/N 470, S/N 21941, JT9D-7Q
747-212B, L/N 471, S/N 21942, JT9D-7Q
Clearly indicated by this listing :
Latest built all pax aicraft (833.000lbs MTOW) are powered with JT9D-7R4G2 engines. (most fuel efficient)
All early built freighters are powered by JT9D-7F engines (MTOW 800.000 lbs)
Most powered by JT9D-7Q engines.
Note : 3 more 747-200 freighters were obtained later :
747-222SF, L/N 673, S/N 23736, JT9D-7R4G2 (NWA : July 2000
747-222SF, L/N 675, S/N 23737, JT9D-7R4G2 (NWA : July 2000)
747-212F----L/N 710, S/N 24177, JT9D-7R4G2 (NWA : Oct 1999