Engine will not start when timing shunt is connected. Indmar 350 Assault

I need help figuring out why my engine does not start when the timing shunt is connected.
Supra Launch 22SSV 2004 with an Indmar 325 Assault (GM350)

Backstory: This fall when winterizing the boat I noticed water in the engine oil. I had an incident when the engine overheated during the summer so I suspected a blown head gasket. This winter I disassembled the engine and resurfaced the heads and replaced all the gaskets. I put everything together and started the engine. As suspected the engine ran rough with only base timing. Now to my main issue. When I connect the timing shunt, the engine will not start. The timing shunt is the correct ABCD-Delco distributor version. (B-to positive and C&D in a loop). When I try to start immediately after connecting the shunt it will fire once, just as if there is some leftover gasoline in the throttle body. When I reconnect the plug to the ignition module the engine fires up. Any idea what is going on and what to do?


**********Mystery solved and I have now educated myself... ****************
In order to set the engine to basic timing mode on EFI models you just need to jump wire A and B on the data connection plug.

Well, you live and you learn and occasionally blow things up...