Any gains from removing holley choke horn?

[PKRWUD]

It's very difficult to turn a vac. secondary body into a double pumper because the passage between where the accelerator pump goes, and the squirter, doesn't exist. You'd need a new bowl and a new secondary metering block as well. The easiest way to take care of the secondaries in a vac. secondary Holley is to change the spring in the vacuum housing on the side of the carb that controls the secondaries. Get a spring kit for $20, and put in the lightest one (white or yellow, I believe). Then your secondaries will open for sure.

As far as the holes in the butterfly valves, just get two correctly sized set screws, and tap the holes for them. Use some thread-locker when you install them.

I clean my carbs in my solvent tank, which has a 50/50 mix of mineral spirits and water. What that doesn't clean, I use a fine wire wheel on, and lots of compressed air.