I would put it back to stock mixture and improve the air cleaner to have a stack at the air cleaner and a much larger air cleaner. The cheap rectangular air cleaners choke the intake air, there is no way to tune that with jets and tubes. I think the Mopar 2.2L used a feedback version of the progressive weber around 1985 on Omni and othe K-Cars. They used a metal air cleaner with cartridge element, it may work much better.
About the timing. The stock 2.5 degree setting is with distributor vacuum hose disconnected and plugged. In your case it is important to know what the cruise timing is, where over heating occurs. The weber may have a different ported vacuum, so you may have to tune the timing off spec. First verify the vacuum dashpot on the distributor functions and does not leak. A mighty-vac is useful as a vacuum source and measuring vacuum. I find it indispensable just like a multi-meter, screw drivers and 1/2 and 9/16" wrenches.
Sometimes when pertronix or even points are installed the screws on the breaker plate protrude such that the sliding to part of the plate is locked, disabling normal vacuum advance operation. An example is removing the screw that holds the condenser and re-installing. Other example is loosing a screw and replacing with one too long. Not having the vacuum advance functioning will result in retarded timing.
If all is OK then I suggest advancing timing a couple degrees, and see how that works for you. Monitor temperature, how the engine responds to throttle and how it sounds. If it seems improved, and the temperature goes down, try advancing a couple more degrees. If the engine starts to have a harshness, pings under load, kicks back when starting, or lopes when coasting the timing is too advanced. There are ways to solve the individual advance issues by modifying curves, but that is beyond the scope at this time. The test is to see if the advance helps to alleviate the heat issue for normal cruise.
