Poor hot idle caused by ethanol gas? Whaddya think?

Here is a 1/2 inch spacer specific to a slant six one barrel.
one barrel spacer
This is not a good idea. It'll screw up your throttle linkage—adjustable if you have a cable-type throttle linkage, but not if you have a rotating-rod type—and it'll screw up your choke (can sorta fix by custom-making a longer choke pushrod) and it'll screw up your automatic transmission kickdown linkage (maybe fixable partway or all the way if you're lucky, but often it's not).