I'll take a shot at this. I think you're describing unrelated problems, but lemme try:
1. "The symptoms....At start up until engine reaches 180* runs like a dream. Smooth, no noise or misfire. As the temp climbs just past 180* it develops a slight misfire, and starts to labor."
>>>This sounds to me like either your carb is too rich or the float level is set too high. When it's cold, having a rich mixture helps it, but when it heats up you seem to be getting too much gas into the engine and it's stumbling. When it does that, you might see a little black smoke from the tail pipe, and your spark plugs will be black and sooty, both of which would support this theory. Pull the screw out of the side of the float bowl and adjust the float until fuel is right at the threads. If that's not the problem, drop the jets down a step and see if it gets better.
2. "Oil pressure at 37psi until then, it drops rapidly to 30, and then more slowly til it levels about 21psi."
>>>This is nothing. When your oil is cold, pressure is higher. As it warms up, the oil thins out and pressure drops. It is a little low but not seriously so. Check your oil level and make sure it's not low. When engine bearings wear, the oil pressure drops. Nothing to worry about yet. I don't think this is your problem if you have a fresh rebuild, unless the clearances were a little on the loose side. Still, that's decent oil pressure. It climbs when you rev it...right?
3. "Meanwhile at the vac. gauge, at start up til 180* rapid bounce between 19" and 20". Havent dialed in the carb just yet. Again, at the magic number 180* Vac still bouncing rapid, but reading 21"-22"."
>>>This kind of sounds like leaking past the valves to me. How are your valve stem seals? Do you get a puff of oil on start up? If not, then you might have some leakage past the valve seats. A simple valve job is possible, but if your engine runs fine, I wouldn't worry too much about it.
4. "Voltage readings, Key on, not started, reading 6.7-6.9 at the coil, immediatly after starting, I'm getting 17.8 to 19.4!!!!!!at the coil. Once the operating temp is hit, I have 12.8-13.9 at the coil."
>>>That's a little strange. Okay, did you put a conventional 12 volt alternator on a 6 volt system? That's sort of what it sounds like. When it starts, the alternator senses a "low" voltage in your 6V battery and tries to charge it. If this is the case, then you're overcharging your battery which will kill it, frying components not designed for 12 volt operation, and overworking your alternator.
Definitely check this out and make sure to run a 6 volt generator or convert your system to 12 volts.
5. "I have repeated this scenario three times, so I dont believe that it is anything internal in the engine itself. Whats happening as it gets up to operating temp? Is this an ignition/electrical, or cooling problem?"
>>>I don't see how it could be a cooling problem. I also don't think there's really a problem with your engine. It may not be perfect, but seems to be happy until it starts getting fuel pouring into the engine. Get that fixed so you don't wash the cylinder walls and lose your ring seal. The electrical issue could be a huge problem if you're running a 12V alternator on a 6V system. Don't fire it back up until that's resolved.
I hope I'm on target with those symptoms. Write back if that raises any other questions.
