OK. Final follow-up on this thread. I just popped out the plugs that I'd put in new after getting the heads back on and before going on my little drive (and a second short drive). For me, this is really the acid test as I've always had an oily #7 plug ever since this whole palava started.
Remember those really crusty black looking piston tops and chambers? Remember how black all the plugs were getting (look at pics earlier in this thread)?
I did a little light reading on that. It's generally a PCV system that's doing a poor job taking the oil out of the vapours pulled back into the engine along with generally poor ring seal causing a lot of excess blowby and crankcase pressure. The oily crankcase vapours are sticky and then soot and stuff sticks to it making the black mess, right?
So I'm thinking that yeah, seems like I've just got a fair amount of that sort of issue going on. But those plugs are looking pretty good now! I'm thinking that I was having all that carbon building in the engine purely on the basis of
* #7 (and earlier #2 and #6) pulling in plenty oil and...
* a reasonably lumpy cam causing enough reversion to "share the love" via the intake to all the cylinders
I'm betting a bit of driving and a few race meets and that soot is going to blast itself out of there.. Or, at least, it doesn't look like it should be adding any anymore now. Maybe I'll throw my can of GM top engine cleaner through it just before the next oil change...
Anyway, thanks tons for all the help from everyone. I declare this issue closed.
Sam