can anyone tell me what I should set timing at for a 74 318? TDC or 6 d TDC?

Forget the manual and "what it says." Many of the '70's stuff was set AFTER TDC or at TDC "for smog." That does not mean it ran. Notice I said ran. If it's not running it does meet the smog test, right?

I would be tempted to "more" as opposed to "less."

The thing is THE TWO DISTRIBUTORS may be different as to advance curve. THIS MEANS that you are just shooting in the dark.