A 292/302 duration cam is pretty lumpy for the street. Even in a large cube motor with good compression, that cam is still bleeding off cylinder pressure at idle.

You idle speed will be higher than stock, like 700 to 1000 RPM or so. You should be running a high-stall converter to prevent "creep" at that idle speed.

Gapping the plugs at .045 is a good idea with HEI. You can also increase your base timing a little to improve idle, like 2 degrees at a time. Retard total timing by recurving the mechanical and vacuum advance. Shoot for 32 to 38 degrees total at 3,000 RPM.

What carb & intake are you running? Large carbs and single-plane intakes don't like to idle. Heck, even the Edelbrock Performer RPM dual-plane intake is rated from 1,500 to 6,500 RPM. Check your idle fuel mixture. Too lean and the motor will stall. Too rich and the motor will load up and stall.

You can also put a check valve in the brake booster line to help out with intake vacuum a little. You can also try a vacuum ball or resevoir that stores some vacuum when idling.

Good luck
Chip

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes