I dont mean to bring a dead thread back to life but I just installed the same exhaust system including headers onto my new 84 chevy k10 and everything fits.
Nothing was wrong with the headers at all. They clear the frame pretty well. Turns out the passenger side of the exhaust was intended to go bellow the transfer case. I took my truck to the exhaust shop and they welded everything good and rerouted the passenger side. They even installed an H-Pipe.
The flowmaster 44's didn't sound as good as I hoped, if I could do it again I would of tried magnaflows. My truck doesn't sound deep or loud at all IMO
But hey you and live and you learn. Just wanted to give some info on all this, the headers turned out fine, the exhaust system turned out good. The mufflers could of been better.........