Installing MSD6AL

The MSD doesn't care if the resistor is there or not.
Easiest thing to do is add a piggyback for the on/off wire.

See the original diagrams I've posted here
for points ignition.
https://www.forabodiesonly.com/mopar/threads/6al2-box-12v-keyed-source.464979/#post-1973002683
or here for magnetic pickup distributor (Looks like your car has one based on your photo)
https://www.forabodiesonly.com/mopar/threads/finding-switched-12-volt-source.469153/#post-1973069957
As far as the fan, my suggestion is ditch it and go mechanical if possible.
Blue and yellow without context I can't help with. If its a '73 and is the ignition branch to the ECU, I would find another power source. The J2 (ignition run circuit) is already heavily loaded in '73. But if the J2 is just being used to trigger a relay, as the photo shows it might be, then its fine.