Thanks for the responses guys.
Grady, hello and hope things are well with you. Everything good here except I am wiped out after finally getting my "Auto Spa" up and running - working 12+ hours, 7 days.
Good advice on the distributor pull, I think I will do that this winter. On the rotor, I have the correct one installed and tried another new one for an S and had the same result, so it is not that.
John, wow - great information. I am not familiar with the SWB distributors, but now that you described it to me, I definitively do not have one. Mine has an Al core and is not black. What I do have is a small raised square piece in the casting that fits into the distributor cap that acts as a "key" to make sure the cap is installed correctly. The cap I have new does not have that notch in. I'll bet it is the wrong cap, when I thought it was correct. It came with a parts cache when we bought a 73S. I just assumed it was for a LWB and did not cross ref. P/N's. Could it be possible that I have some other distributor in there? I am really curious now and am going to get the numbers after work. Thanks for your help and detailed information.