Good discussion and interesting project your working on Mike.
I am just getting my 76 B210 running, for general use with decent gas mileage.
I used the car part locator to find and buy the 'mileage' differential.
I found 2 NEW in the original factory crate A12 engines on Ebay. I bought them both. The guy had one to run all his sewing machines, had the extra engines as back up, but the original engine was still going strong so he sold the others. Was a bit of good luck for me.
The A12 uses a cam with less intake exhaust overlap than the A14. You say the engine has ping detonation. Setting the quench clearance between pistons and cylinder head will help stop this. I set my pistons 0.006 inch above the deck (top) of the block. I measure all my head gaskets for uncompressed thickness. Most are about 0.048-0.050 inch thick. Compressed I have 0.040, which leaves 0.034 quench clearance. Using KB-silvolite compression ratio calculator online, my static compression is only 10:1. So subtract 1 point for aluminum heat dissapation leaves me with only 9:1. I was hoping for better, but I did want to run on regular pump gas---NO premium fuel. I saw on the net somewhere that custom made flat top pistons are available for Datsuns.
One of David Vizard's books says they ran as little as 0.026 quench, but he suggested about 0.030 was probably pushing it for street use with OEM parts.
I am also using a round port MPG cylinder head. I have an older A12 head, has even more quench pad than the MPG on the spark plug side, but it has loose intake valve seats, and needs some welding to fill in a porosity problem that came with the casting. The A12 head has 24 cc combustion chamber.
They say ideally the quench pads should be same size symmetrical on each side of the valves like Ford 351 cleaveland aftermarket heads.
Vizard also says to reduce detonation the engine needs the coldest intake charge possible, but that goes against the gas mileage issue... or does it?? I agree with the discussion of fuel atomization, but not sure if high compression and hot mixture go together.
Probably a dumb question.. have you removed the 5 mph bumper structure?