The 250's all were marked on the timing cover tab for 0, which was TDC, and depending on the year were marked every 4 degrees both before and after. Some were barely legible when new and years of grime and rust make them difficult to see. The TDC "0" mark on my 67 cover is the 3rd point up from the bottom. The point being at the outer edge, not the bottom, of the V. This particular cover is marked every 4 degrees at the points from 8 retarded to 12 advanced (8 - 4 - 0 - 4 - 8 - 12) . Every line on the tab represents 2 degrees but only the outer edge points are stamped. This cover has a total of 5 points at the outer edge.
When I build an engine I carefully run a hacksaw through the TDC line on the timing tab and from then on no matter how much crud or rust or how bad the paint gets the slot is always visible to line up with the degree marks on the balancer. Heck I even do it to my stupid V thingys too!
Hope this is some assist to you.
Mike
