Wow, quite a varied response which is good for discussion, however, I've rebuilt a lot of Holley's in the past 45 years. I was shown 'hands-on' by some of the best back in the day, and there were a few things that they all seemed to express as vital to a great rebuild, not just a good rebuild. If you want a quality rebuild that retains the original FIT and FINISH, patience is your best friend. Do not use any type of spray carb cleaner if you don't want to destroy the original carb coating/color. Back in the day it was economical to buy the GUNK 5-gallon bucket of carb cleaner and let it soak overnight, unfortunately today, carbs are like hen's teeth in the chain parts stores, and so are the GUNK 5-gallon buckets. You can use KROIL, as mrhemi
mentioned, or the 3-IN-ONE variety as pictured. Soak every gasket mating section liberally, occasionally rolling the carb until you've penetrated (soaked) all 4 sides. No metal anything to pry apart any sections that are stubborn & froze, remember you're using penetrating oil which is the patience part of the job. You'd be surprised how the slightest gouge to just the right surface edge of a metering block or carb body could adversely affect the final function of your rebuild. Even if you successfully pry the sections apart without any marring, it doesn't take a lot of force to actually warp a fuel bowl or metering block. So far, everything I've mentioned, both good & bad, I've experienced while going through the learning process over the years. After everything is apart with, or without, carb cleaner as pictured, get yourself a bucket, or better yet, the kitchen sink and fill deep enough with warm water & dish detergent to completely submerge every piece including the main body. Get a selection of children & adult NEW toothbrushes with good stiff bristles and scrub away - literally. Completely rinse everything with clean running warm water, shake & wipe dry everything as best as you can, then place the main body, metering blocks & fuel bowls on a dish towel covered baking pan and place in the center of the oven with the temp at it's lowest setting & the door propped open 6"-8" and give it an hour or two, remember the patience part? All soap & water washing, and all baking is only to be done after all the removable parts have been removed (metering jets, power valve, needle & seat, float, check balls, etc.). NO plastic anything goes into the oven for drying. Never use compressed air to blow water from any internal passages since this can introduce moisture from within the air lines. When it's time for reassembly, screw & attach everything by hand first to insure there's no chance of cross threading anything. Carburetor metal is soft & non-forgiving, patience. Do not torque anything either, hand tight with a screw driver for metering jets & bowl to body screws (tight, but not torqued), same with wrench on the power valve, one snug pull. Good Luck!