BB exhaust studs

I'm trying to install Schumacher headers on my Duster w/ a 400 engine, using studs instead of header bolts. I bought a set of studs (2") that matched a couple I found here but they're too long on the head end and won't let the header past to be installed.

The heads are 915s and the studs only went into the heads for about 3/8" before stopping. The shortest studs I've found so far are 1/2" on the head end so those won't thread all the way into the head either. (1-1/2" total Dorman 675-098)

Does anyone has info on stud part numbers that will work?