First hit on the dyno

TT5.9mag said
I thought the same thing. Isn’t the 400 the go to foundation for all the 451 builds?

Yep! With a 4.25 stroke and .010 over, it’s a 502.

And 383 -> 496 (4.250" stroke/6.535" rod)
or
383 -> 426 at the stock bore,
438 (4.31 bore, 3.75" stroke/6.760" rod)

So those short deck blocks are worth a little something after all. LOL!