I replaced the CI MC on one of my hot air Rivs with an aluminum one. I dont recall the exact model but it was a full size GM with HB, maybe 1983-1985. I'm not 100% for sure but I think the bolt pattern is the same on the HB so maybe the aluminum 1" MC from a B-body will bolt on. The only 4WDB MC I can think of off the top of my head would be the 94-96 Impala SS and 9C1 cop car. Also IIRC on my Riv the reservior on the aluminum MC was rather big as in being taller than the average reservior and was made for a MC that sits horizontal but I think all HB are that way instead of being inclined like the vacuum booster set up.