Magnum and Wiring Swap

I remember seeing that the GM filter/regulator is higher than what a Magnum's fuel pressure is. Your explanation of the fuel being pushed past at low duty cycle makes sense because the exhaust smells rich and economy doesn't seem very good, comparable to the old 318 that was carbed. I know with a 904 LU and 3:73 gears it's not going to be awesome, but it's around 10-12 MPG right now.
It does seem to be running better now that the seal was replaced on the MAP connector. Occasionally it will pop (not sure if out of the intake or exhaust) on hard acceleration. Also, there is a 3-5 second rattle on light acceleration when the engine is cold. It doesn't sound like top end noise, possibly pinging? I'm running 89 octane. Maybe without a VSS it's not advancing the timing? I'll get a video of it soon.