[priobe]

I am sure others will chime in.

I dont understand why you want to run 2 pumps. The rating on the Holly should be more than enough supply for the carbs. If you are running them in series the mechanical pump will restrict the Holly pump.

If you are running them in parallel then they should be the same exact pump.

As for the pressure reading I would measure the pressure right before the carb. You should be interested in how much pressure the carb is getting.

If you put the gauge before the mechanical pump you will only have a reading from the Holly pump.