75 duster slant six weak spark

Yes, the coil + voltage should be close to the battery voltage when cranking; it will liklely be < than 12v since the starter is loading the battery but your 9.5 volts seems a bit low. It could be:
1) the brown wire through the bukhead connector (IGN2) has a problem
2) the ignition switch
3) the power into the ignition switch.

Do all of your spark test WITHOUT the spark plug. Jumping an .035" gap in open air is meaningless; it takes lot more voltage to jump that plug gap in a compressed fuel/air mixture inside the cylinder, so looking at that small gap in open air does not mean it will do that in the engine. Pull the spark wire from the center tower of the distributor and place the end of that wire about 1/4" from metal and test in that fashion. A good stock system will jump that 1/4" gap in open air with a hot looking spark. (This will isolate the distributor cap and rotor out of the problem too.)

Your best test of the coil by itself is as follows and will establish if the coil is good or not:
- jumper the coil + by itself to battery +
- set up the coil spark wire as above with a 1/4: gap to metal
- jumper the coil - to ground for a moment to and unground and it will spark when ungrounded; make sure you are insulated from this jumper as you can get a jolt from it

You ought to recheck the resistance through the coil from coil + to coil -. Set the meter to the lowest scale (it may be 200 ohms) and recheck that resistance with all other connections to the coil removed. You ought to measure 1 to 2 ohms. (Make sure you connect the 2 meter leads together first, record that reading, and then subtract that from the coil + to - reading.) (The .002 reading is likely 2 ohms but make sure.)

Finally, did you set the reluctor gap in the new distributor to .008" with a non-steel gapping tool? (Brass strip or matchbook cover)