All this seemed to improve things a little, but the car still "popped" under full load (acceleration/ up a hill, etc) and in general felt worn out. Then I remembered that last summer, even though the car was overheating, it seemed to run best when it was pretty hot. After my engine rebuild, I had the radiator (a four row) rodded out and the block back flushed, and added a Hayden 6 blade plastic fan to replace the stock steel four blade. This definitely improved things in hot weather (ran cooler) but it was still overflowing & loosing coolant. That problem was solved by installing a simple overflow tank to the radiator (I think it cost me $10 or less from Pep Boys). I've never lost a drop of water since, even in hot weather. I would recommend this to any Alpines out there as your whole cooling system will work better. Anyway, now the car was running much cooler. It's since turned a lot cooler (for Los Angeles) and has been in the 40s to 60s the last few weeks.
In this weather, with my extra efficient cooling system, the water guage (which I had checked and is suprisingly very accurate in that the needle straight up represents 180 degrees water temp.) barely reached 1/4 of the way to the right off the peg. Last week I remembered the much better engine response when it ran hot. Here's the fix: All I did was take out the 160 degree thermostat and put in a 180 degree unit. The difference is dramatic. Much better acceleration, no more backfiring at all, the heater gets hotter, better idling and much quicker warm up in the morning.
We all get so used to trying to get our cars to run cooler that it never occured to me I had succeeded too well. A couple of you had mentioned a similar backfiring problem, so you may want to check this out that you're reaching full running temperature, especially in cold weather.
Hope this helps someone else out there. Thanks again to everyone for all the help and advice!
Regards, Steve Sage