340 Chugging instead of Reving

I think you're onto something with the reluctor.
I'm not familiar with that distributor, but is it possible the pickup wiring is backwards? I seem to remember if it's flipped, you'll get more "advanced" spark when looking at the rotor and reluctor relationships to the cap and pickup. The spark will also be shitty - but no idea if that applies to your Dist?
Typically, a magnetic pickup should be wired in the direction that results in the least advance (most retard).

Figured I'd mention it, if it applies.