Almost got it.
This is the factory distributor for 1974. It WAS a Delco-Remy points distributor, and was upgraded with some aftermarket pointless ignition system.
It is NOW a factory Delco points distributor that has been converted. The conversion is an oddball that I don't recognize - likely extinct.
You now have the FACTORY distributor cap (Delco type) and the FACTORY rotor (Delco type) and the FACTORY coil. There is nothing oversized or upgraded about these parts.
The Duraspark parts are completely different and will not fit on this distributor.
The name "Hall a tron" suggests that this system uses the Hall effect as a trigger. This works fine, but it's an oddball today. Both the HEI and the Duraspark use the
variable reluctance principle, which is still in common use today (along with optical triggers). Likely obsolete - so I kinda think you should junk it all.
I would not use these parts - if the electronics fails, you will be forced to convert to some other system, because this stuff is no longer available.
We do not know if this converted distributor is compatible with the MSD 6A ignition box. I don't think the MSD can be triggered by a Hall effect distributor.
Maybe ... you could experiment, but your uncertainty indicates this may not be the right path.
I suggest you replace it all. You can probably convert the distributor back to points if you want. Points will trigger your MSD module.
Or you can use the Duraspark system parts (buy a Duraspark distributor, and your choice of parts to go with it), with the factory module or a MSD module.
Or you can buy the aftermarket HEI distributor, which has its own module.
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D