I'm not absolutely sure that the head resurface cured the problem. (As you may recall, I was exchanging oil and water during my last outing at the track.) I've run it about an hour this time (garage runs only), and I see a trace of oil in the overflow bottle and at the top of the radiator. This *could* be residual oil from last month; I tried to flush it all out but may not have gotten it all. I'm going to run another bottle of flushing agent through it and see what happens. But last month, I really didn't see large amounts of oil in the water until we ran it on track for 15 or 20 minutes. That day, after about 80 racing miles, I ended up with maybe 1/4 pint of oil in the cooling system, and lost a pint or so of water to the crankcase, much of which ended up in the crankcase ventilation "catch can".

My working theory at this point is that the exchange was taking place through a common duct (leaking head gasket or cracked block or whatever). With the engine running, lube pressure would be higher than cooling system pressure, pushing oil into the cooling system. Then after shutdown, residual cooling system pressure would take over and bleed water back into the lube system through the same orifice.

Fuel: I use a 50-50 mixture of 110 octane (leaded) racing gas and 91 octane unleaded pump gas. This mixture keeps the cost down a little, but seems to provide ample octane for the 11:1 CR. The previous owner ran the same basic mixture with no apparent problems for 5 seasons, so I chose not to tamper with success. Also (according to the p.o.), there was apparently some extensive dyno work done by a group of ITB racers back in the 90's that pointed at this sort of mix as cost efficient, with no power loss. I dunno... like I said, I'm just not prepared to experiment, as there is no way I'm going to be able to hear any detonation/pinging noises with my current exhaust setup.
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1971 142E ITB racer, 1973 1800ES, 2002 S60 T5