I understand the BB is where the shop manual says to set timing to. Shop manual also states it should be running 5 degrees advanced when idle is below 600RPM. So does that equate the BB to being 5 BTDC? Mine does not have the UIC stamping. It has the triangle for valve timing, 2 vertical lines, the BB, then another vertical line. I'm thinking the vertical lines are 5 degree increments. The reason I'm asking is my truck is stock but for the rear end has been swapped out from 4.56 to 3.73 gearing and when I set timing to the BB it idles and runs smooth as silk. But is gutless above 25MPH with the lower rear end gearing and I can't even take a small hill. I'm currently running by my timing light 3 degrees advanced of the BB which gives me better highway power but the idle starts to suffer. What I want is the smooth as silk idle below 600 per the manual but I need a steeper advance curve when I come off idle for highway driving. So I'm looking at the Pertronix billet distributor with the recurve springs kit, advance limiter, and vacuum advance. But I would like to establish baseline timing off of the BB so I know what my actual timing curve and all in advance is which from memory is around 24 to 28 degrees. I can't know where I'm at if I can't establish if the BB is 0 or 5 degrees advanced.
