The exhaust is the 64 race Hemi manifolds, butchered up to be able to use on the dyno. I would guess that this was a very very early fire up and run test, maybe some durability testing. But not a real horsepower test with that exhaust system.

1964-Hemi-circuit-racing-eng.jpg

[img]http://i.imgur.com/boeexFms.jpg[/img]
31 Plymouth Coupe, 392 Hemi, T56 magnum
RS23J71
RS27J77
RP23J71
RO23J71
WM21J8A
I don't regret the things I've done. I only regret the things I didn't do.
"Wise men talk because they have something to say; fools because they have to say something. ~ Plato"