My experience is powdercoating Rochester 2GC 3x2's but it might also apply to your Holley's, if you go the powdercoating route.

I built my 3x2 set from swap meet carb cores. As such they all looked different in their finish. Two of the three carbs came back looking great but the body casting of the third carb came back all bubbled up. The coater did not even mention the poor quality coating, until I unwrapped it at home and returned it to them for a re-do. It looked almost like paint after the remover was applied, Yuck!

Evidentaly, what happens is on some the die cast items like carbs the metal "casts off gas" when its heated for curing the powdercoat causing the rough surface. The cure was to strip the carb, and place it in the coating over to expel the gases before it was then recoated. Their second try came out great.

For the local Orange County guys, this coater was NOT Embee or Ikon, both of which do great work.