Asumeing you have a low compression motor as in 8 to one or so then bumping it up to around 10 to one would help smooth it out. Advancing the idle timing to 18* or so should help it how it is but it is never gonna be smooth. Mabey some poly motor mounts will keep the engine from shakeing so much but will instead shake the car more. A 4 corner idle circuit carb should in theory help but never worked for me. Last thing I can think of is to turn the idle up to around 1000 RPM, mabey more if you can stand it.