Larry, A couple months back I researched coils to understand the numbers better. I never found a definitive meaning to the B-R. One mention it may be Ballast Resistor which I did not understand why it would be on the coil. I did notice that earlier 60's GM had coils embossed with 12V or were blank. Then later they came with a BR and even later B-R embossed. I had searched several different GM classic car forums.
Scott, thanks. I suspect it may remain a mystery when it may have changed. I just checked the SUN sheets for '68 and '69 and they only showed the 288 and 410 respectively like the AMA and Service Manuals. Interestingly, the specs are slightly different for the two coils and the ballasts also had slightly different resistances. Perhaps there was also a different resistor wire for each? I suppose I will still search for a 288 for my Jan '68 build. I have also asked a couple vendors to see if their coil repro manufacturer could make a 288 like they have several other Delco Remy coils.