HEI for the late L6 came out in very late 1974 and ran through about mid year 1976. It is a bolt-in for any 250/292 cid with points. Find the 20GA pink/purple wire that comes from the bulkhead connector and goes to a connector near the coil where it becomes yellow and forks to the stock coil and the starter. Remove it from the bulkhead connector on. Get terminals for the bulkhead connector from NAPA. Part numbers for the male and female pins are 72145 and 72147 respectively. Install a 12 GA (minimum) wire in place of the one you removed, and run it to the IGNITION connector on the HEI cap or POSITIVE on the HIGH OUTPUT remote coil. While there MAY be some smog control L6 HEI distributors, I have been unable to find any evidence in GM parts books, but you CAN get an adjustable Vacuum can and spring kits. Just a note, but on the cab side of the bulkhead connector, EVERY truck that came with a late L6, that's '62 on, that I have personally worked on has a 12GA to the ignition switch! You get more bang for your buck doing this than anything else to your late L6! Also, I have converted remote coil HEIs to "Coil in Cap" HEI by changing the cap and coil. I'm sure it will work the other way, too, but I have never tried it. The HEI gets its reduction in pollution from its clean burn, not it's advance curve.
Best wishes,
Les
