[red77911s]

My 77 takes thin flange HE's (it's backdated to 73 style HE's) but from what I've read thick flanges will work if your exhaust head studs are replaced with longer ones. sounds like your studs are the long version. On the other hand, thin flange will work on the long studs though you may want or need to stack washers or make spacers so you don't have to screw the nut so far down. curiously my car came with one SSI and though it was thin flange my particular exhaust studs barely reached through it, one of the nuts was only half on, SSI's have a slightly thicker flange than OE, so I found a stock one to replace it. All SSI's appear to be identical internally.