Me too, there's very little info on 74; even less on the HEI and BW change. I spent a few bucks and a bunch of time researching the HEI introduction. There's allot on the unitized PMD and the first attempts in the 50's and 60's but with management changes that year at AC Delco it all got lost. Along with the open hole in the fender. I saw one mention of that being coupled with fender vents in 75 for a pressurized induction. Who knows.