My notes below

1) Going from 11” drum brakes to drag race weight disc brakes
My experience was going from ten inch drum brakes to four wheel disks, I saved forty pounds but did not pick up any ET or MPH that I could tell. However it sure stops a lot better and I would do it again. Dual calipers on the back are very much like having a transbrake.

2) Merge collectors vs. standard
I have them on a 2 hp per CI small block but no AB tests.

3) Eliminating the water pump drive ( going to electric drive drive )
There is a good episode on "Engine Masters" where they tested this, big gain if I remember plus the ability to cool faster between runs and mentioned by Bad340Fish. Meziere would be my choice if for no other reason their great support.

5) 904 vs 727 with 2.45 low gear. ( heard .10 e.t. reduction )
The low gear may or may not help you but the 904 is worth at least a tenth.

8) Diamond piston versus old cast piston used in item 7.
In my opinion anything you can do to raise the compression, use thinner rings and have lighter recpicating weight will help. Even at the same horsepower things that will help the engine accelerate faster will help on the track. (My opinion).

You did not mention it but in my experience, documented on the dyno, vacuum pumps make horsepower in engine with gas ported pistons, thin rings and low tension oil rings. Your mileage may vary.

Good luck and let us know your experiences.

Bill Lamb