Intermittent slow crank when coil wire is plugged in to the dist

This is a 68 Barracuda with 408 blueprint engine stroker with their Ready to Run distributor that comes with an internal ignition. No ballast. I rewired a good amount under the hood and dash and swapped out the bulkhead connectors not too long ago. I'm just now attempting to start the engine for the first time.

Symptom is the starter slow cranks about 4 out of 5 tries with the turn of the key. If I use a remote starter on the starter relay or I unplug the coil wire from the distributor, it'll crank just fine.

I did identify one problem, which is I'm only getting 10v at the starter relay on the "run" wire when I have the coil wire unplugged and the engine is cranking normally. When I plug the coil wire back in, I see 7-8v or so.

Anything else I should look for on top of ensuring all my connections and continuity look good? I'm not understanding exactly why I'm getting less voltage at the starter relay connector when I have the coil wire plugged in vs. when I don't.

I have gotten the engine to start a few times and got the timing dialed in close enough to at least have it idle on it's own but this problem is puzzling me.