"pull the air cleaner(s) off after it has died and look for or stick your finger down the end carbs and see if one is wet.
If you even think the vacuum modulator is leaking on the transmission, change it. Should cost about $10 and about a pint of ATF when you change it. Make sure the old o ring comes out, they like to stay in the case"
Had a "fun" afternoon. Long story short, did not seem to have wet end carbs, actually the center was not all that wet either. Maybe not enough gas from the fuel pump?? What is the fuel pump model number that should be used on 421 Tripower? Changed out the vacumn modulator. The vacumn seemed to bump up a bit, but after it got hot (approx 15 min), when put it in drive with foot on brake and sat there for awhile (like at a long light) - it would start to stumble a bit, noticed a drop from 10-12 HG to 10-8, then it would go back up again to 10-12, after a bit, it did a big stumble under 8 hg and died.
Story of the afternoon - started off good, Had two projects to work on, the suggestions for the GP and flushing the fuel lines on the 2+2 and getting the carbs off to "61-63". Got the 2+2 carbs off and drained so they could be shipped. Next the GP -struggled getting the bolt off the modulator, but finally got it off. Did not have the drain pan positioned just right and the first blast of tranny fluid went on the floor instead. got the modulator off and took to 3 part houses. Autozone not in computer, not in their warehouse, they dont order...Fine...NAPA - not in computer, trouble finding in book, not sure if they have in warehouse. They suggest trying to find one in a junkyard. WHAT??? Guess lots of 66's lying around in yards. Might as well get my air cleaners there too. Finally O'Reilly had some...back to the house, put it back on and test drove the car- looked promising for a while, then after it warmed up...result noted above
When cleaning up, pulled the drain pan from under the car and somehow managed to get my hair in the tranny fluid - lovely.
Then back to the 2+2, unhooked gas line at the tank, the rubber hose was cemented to the line - took forever to get it loose, then of course the gas runs all down arm and onto shirt. Unhook the gas line at the fuel pump after fighting with hose clamps that are positioned so only a contortionist can reach with a screwdriver/nutdriver. More gas running down the arms. Blew out the line to the tank, ran gas thru the fuel pump to flush it out and got everything back together. Did not notice any crap in the fuel - so the carb crud must be old. Sending the carbs out tomorrow. I now smell much better after cleaning up and don't recommend tranny fluid and gasoline for your hair or skin treatments
If anyone has any other ideas for the GP stalling problems, let me know and will try that next weekend...