Rough idle... only when warm.

Could be a few things:
[1] Lifter preload [ bottomed out ]. Unlikely but possible. As the engine heats up & parts expand, bottomed out lifters have nowhere to go & stop the valves from seating.
[2] Carb. Remove it & disassemble. Unlike brand H & clones, you won't need gaskets if you are careful. Blow out passages with compressed air. In the primary clusters, you will see a thick & thin brass tube hanging out the bottom. The pinched lower end of the thin tube is the idle fuel feed. Poke a piece of wire in it to make sure it is not blocked. Be careful, the boosters have a L & R, not interchangeable. Re-assemble with 7/16" float setting. Set idle mixture screws 2.5-3 turns out from seated.
With the carb back on the car, loosen the tops [ 2 turns on the screws ] on the metering rod pistons. Swivel the tops slightly so you can see the piston but it remains captured. Tighten screws.
Warm up engine & adjust mixture screws [ in gear if auto ] for smoothest/highest idle speed. Look at the pistons; they should be down & not moving. If they are moving, you need softer step up springs. If they are moving, use a thin screw driver or wire to push the pistons down. If the engine note changes, it means the pri throttle blades are open too far at idle. This can be caused by a big cam, worn cam, PCV that is oscillating & not closing [ usually caused by low vacuum from big cam ].