Technical timing cover

I have an aluminum timing cover for 49 to 53 that has two holes for the timing pointer. One says 8RT and one says 0BA. The holes are about 1/4 " apart. What is the difference? I'm putting together a 1BA block. Isky Max 1 cam, 080 over pistons, Red's adjustable hollow lifters, 3&3/4 crank.
Bubba's Chev. dizzy. Any help would be appreciated.
Thank you,
flatheadnut0

 

with all the different crank pulleys, I'd be installing it TDC and making sure the pointer lines up with the notch on the crank pulley. If not, either adjust the pointer location, or re-notch the pulley. Either way, you're sure the timing mark is correct. just seems logical to me....should idle at 2 BTDC.

 

The '48-'53 trucks, along with '49 Fords and Mercs, used large OD sheet metal 5/8" wide-belt crank pulleys, while the '50-'53 Fords and Mercs used smaller OD 3/8" belt cast iron stepped pulleys, and the reason for two pointer locations on the two styles of aluminum front covers, as they could be (and were) used with either pulley. The timing bumps, however, are two degrees BTDC on all late pulleys, not TDC.

 

Thank you V8 Bob. Never too late to learn something.
Thank you,
Flatheadnut0