HELP! Slant 6 just doesn't want to go!

Wow!! long read for me but I think it could be one thing..... you do know the bottom of your distributor has a adjusting area also If you have it running and the distributor is close to the mid range of adjustment you are good there

Know if you have it going as far as you can.. one way.. and it run's but will not run good if you pull it back a bit .... your bottom adjustment is off maybe ... pull the distributor out and adjust the bottom so you can get more advance or bring the timing down.. Just a thought ... I hope this threads ends well