Slant six 500 cfm edelbrock jets and rods

I have seen over 20 with a 318smogger on straight hiway, so I'm guessing you could go leaner. But you'll need plenty of ignition timing, and it really depends on a lotta factors. I once squeezed over 30 out of a hi-compression360, point-to-point-hiway.
Rpm is a killer, as is; speed,load, and lack of timing, not to mention; the engine temperature, the cam, the exhaust, and the air density.
18.5 is doing pretty good. At something like 2300@65, she might want something like 48 to 54*,total timing,possibly even more; Sneak up on it. is

But I wouldn't mess with the cruise settings until the power system is dialed in,cuz you just have to start all over every time you change the primary MJ;or every time you recurve the distributor.