I've really got my 2.0 pretty well dialed in. I synced the carbs about a month ago and it runs noticeably smoother.

Still rough when it's cold, and still a lot of popping noises... which brings me to the topic at hand. I know it runs a bit rich, and I've sort of dismissed the popping noises since it's done that as long as I've owned it (2 years).

However, I'm now noticing a significant amount of smoke in the cabin. It seems to come from underneath the dash (footwell vents?) and it's tied to engine RPM - nothing at idle, but noticeable immediately after revving the engine.

At first I thought it was electrical smoke, since it seems to emanate from near the fuse box, but all electrical still seems fine - not to mention it's clearly tied to engine RPM and it's visible on both sides of the cabin. Doesn't smell like electrical either.

I'm going to make time to bring it to my mechanic soon - and in the meantime, most of my driving is al fresco, so I'm not worried about asphyxiating myself.

Does this sound like the HEs? (Stainless) Am I doing further damage by driving it? Given the cost of new HEs, presume I'll opt to fix these, if that's possible/reasonable...

Worth noting - Like most, I do have a minor amount of oil leaking. Is that the source of my cabin smoke?

Oil could be dripping on the the HEs and that may be your source of smoke. I also have seen SSI exchangers crack, but you would hear an exhaust leak if this is the case. You may not see the smoke at idle since the fan is not spinning too fast. Do your heater boxes fully close? You could temporarly remove them until you fix the oil leak or what ever the damage may be.