Spark retard is a smog control function. As John said, you want spark advance. The stock carb and distributor are totally unsuited (in the stock configuration) for proper operation without the smog gear.
You can't get proper vacuum from the stock carb, because the vacuum ports are not drilled in the correct location. Contact Jim Chenoweth ( FJ40Jim@aol.com
) about modifying your carb for vacuum advance.
It sounds like you have a Federal spec distributor with retard for smog and advance for High Altitude (vac hose on each side of the bellows). Even if you get proper vac to the advance port, the advance won't be of the magnitude a properly designed vac advance system would have. I think Jim C. can also rework your distributor.
Contact Jim. Tell him your situation and ask his opinion. He's a goldmine of information, he's very generous with the information, and he'll tell you straight up. His prices seem pretty expensive, but after he's done you'll have a vehicle that operates the way you want it to and you'll only have to pay for it once.
Just my opinion. HTH.
P.S. If you need info to connect stuff stock, I have all of the diagrams for '78 and I have a one-owner '78 as a reference.