I've got a 1998 malibu response with effectively a marine-cammed SBC350 in it. Ran great and died when hot twice, and now I have no spark, at all.

I threw a new coil at it, to no avail. My current test setup is:
 
- single coil wire straight to a spark plug, sitting on a bolt on the motor as a path to ground (this bypasses the cap and rotor)
- Distributor pulled but plugged in, rotating it by hand
- key on, all safety switches in their working position

I've tested and I see 12 volts to the coil. I've also tested the distributor with a test light, and it grounds the C pin as it rotates, as it should. The ECU is alive, because it's firing the fuel pump and the injectors as I rotate the distributor. But yet I have absolutely no spark.

Edit:
If I ground the coil manually with a wire, I get a very strong spark. The wire between the C pin of the distributor and that pin on the coil tests out with continuity using a multimeter.

What further steps can I take to diagnose this issue? Every component seems to be in working order, but when they come together, something breaks.
 
Also to note - it's a 98 GM HEI ignition module. Every mechanic I've spoken with thus far curses that particular module as being an unreliable, untrustworthy piece of junk. I'm tempted to blame it even though it tested fine, but that costs me 350$