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

Well I just retested the timing and I had it set at 10 d BTC.
I dropped it to about 4 or 5 d BTC and the car seems to run fine still, quick response off the line and no hesitation.
There isn't someone who knows what the manual says the timing should be set? Just to get an idea where to start ? My manual only goes up to 1970 and say's 2 d BTC. then 71 say's ** under timing ? This is a 74 Probably no difference? Not to sure. Thanks