Do they actually make headers for those engines?
If I were to do anything to one of them, it'd be pretty much exactly what crazymoparguy lined out. Nothing that would alter the driveability or characteristics of it at all, other than adding a little power.
There's a complete longblock for sale on ebay in Alabama right now for $760.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
| 
