I went with the 1/2" Summit phenolic (wood/fiber/layered) looking spacer and it leaked. I must have rec'd it that way from Summit considering that it did not last for more than 100 miles. I then went with the 1/4" Mr Gasket Heat Dissipator (Jegs #720-86 @ $13.99) and have had no probs since. It is the one that has a gasket, aluminum, gasket, etc. BTW, if you don't put something between the carb and intake you are running the risk of warping the base plate of the carb. Especially if it gets real hot.
1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers