Hi, I'm having some heat soak issues and I'm wanting to install a phenolic carb spacer under my carburator ,but not sure which one would work best on my car, 4 hole or open.I have a 390 with a Luniti VD-FE-284 cam, Holley 750 carb  with vacuum secondarys on  a streetmaster intake,headers,D2t heads,4speed,with 350 gears in a 64 Galaxie, any advice would be appreciated.thank you