A while back I had this mystery: on an engine that I was replacing the HEI in someone pointed out that the existing HEI was an even firer not an odd fire. I had assumed it was an odd fire because it was the stock engine in a 71 cj. The engine ran great with the this distributor. When I brought the distribitor to NAPA they confirmed that it was from an even fire 75 buick motor. I replaced the old HEI with the same model as I had removed
I believe the usual indicators that confirm whether or not you have an odd fire motor is the unique pattern of the plug towers on the distributor; that the timing marker on the odd is cast into the timing case cover as opposed to being bolted on and that the cranks shafts for the two engines are different. There is a picture of the two cranks side by side in the V6 Engine power book whose title I can't remenber at the moment.
While doing the time chain replacemennt I took some pictures of the crank. It appears to me that the crank is an odd fire crank. So there is still a mystery as to how an odd fire motor can run well with an evenfire distributor.