If you switch the polarity of the pump it migth start working backwards. but the propellers are not designed for a reversed flow. There are other unknowns too. There is no cross-water passage in the intake. It is the flow passage within the pump that points fluid tp heads first. I am not sure how hard will be to retrofit regular SBC waterpump. Than it might work. You will lose the extra advance, cooler heads give. The only drawback of the revese flow system is fuel evaporation. I will test warmer thermostat. What helps best is not the overall coolant temp, but the heatsoacked heads. I guess the heads run good 10-20 degrees less than the block. That is why the coolant gauge on f-bodies always runs much lower the pcm measured temp.

Why not run some PWM relay to slow down the coolant flow, at warmup and at highway cruise to regulate temp above thermostat rating. Some inelligent control algorythm will be needed. You will extend the life of alternator too.

I am sure if we play with the transient fuel tables some improvement can be made. Leaving more fuel soacked heads. Another issues that is not discussed is the spary pattern of the injectors. Those ls1 style injectors can spay sideways and the fuel not hitting hot intake valve. I didn`t check mine, they might contribute to the crap run.
I think the stockers have a cone spray, at the correct angle. I might try bumping fuel pressure to see if that helps too. Hope the pump survives 3.5-4 bar at idle for the test.

If you have the time you can command open loop and turn on the evap. Watch for map drop. If it drops a healthy 4-5 points than a evap patch is on high priority list.

I am interested to measure spark duration for the same coil with plugs with different materials. If the resistance is great it is likely the discharge time to last longer. The platinum with dot pluck should always discharge around the dot pluck since copper have less resistance. Is it made on purpose. I have seen heavily worned plugs. The copper core was rounded around the pluck. That dot might be just for longetivity combined with the less resistance of copper. Also the color of the spark can give some clues but the spectrum must be linked with the energy output. Only pressure chamber will sort good and bad plugs. At least 12-16 bars to simulate cylinder chamber.