Timing Pointers....which One??

So I am looking for a timing pointer for my engine, and I keep seeing things like- "fits a stock ford block with the b key at 11 o clock position", or " fits c key at 10 o clock position. Whats that mean exactly?? My timing cover is an older style with a small bolt that runs vertically in between where the two mounting holes will be for the pointer base...

The motor seems to be at tdc at the 11 o clock position according to the dampener...

thanks guys