I just used an old 440 block when I had my car at the chassis shop for the cage and motorplate setup. Bolted the hemi heads onto the 440 block, sat it on the factory wedge mounts for motorplate positioning. Then hacked off the driver's side mount on the K frame to make sure the headers cleared.

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