from what i know, these blowers were originally built by B&M with a 6 or 8 rib serpentine belt set-up with a 16 rib optional...when Holley bought them out, they changed over to an 8mm set-up (much better)...i have a Holley 420 with the 8mm set-up with a Superchiller under it mounted on a special designed for it manifold with a v-shaped floor (^)...better fuel distribution vs the old style plain flat floor...also...the top of my blower has the carb flanges built in to it for 2x4 4150 carbs to run in-line or sideways...i'm also told, these blowers are a cross between a 671 & 871...when i get my 496 together, i plan on running this pkg with either 2 Holley 450 DP or 650 DP mech sec carbs @ 5% under driven...i dont know the capability or max boost etc of these blowers, but, i would think they will handle quite a bit of boost...there is (i think) some one on the boards that is running one of these, maybe more...they may read your post and respond...i hope this helps a little
