Now that everything is perfect, I want to screw it up.

I feel your pain. I am also afflicted with terminal inability to make decisions.

I'm a numbers matching guy myself, but I think a numbers matching engine in a car with fuel injection, an upgraded transmission/clutch and so many other upgrades defeats the purpose. Either go all original to appeal to the original crowd, or go with the 360 to appeal to the pro touring crowd. But don't go for the mushy middle.

Save the 273 block in case somebody wants to put it back original in future.

If you're looking for a rationalization, consider this: a 360 should have a much higher power to weight ratio than a 273. That should appeal to your love of efficiency.