5.7 heads on a 6.4 short block?

Block ID is stamped on the block just above the oil pan rail on the passenger's side, or is on a sticker on the valve cover for a 5.7 (According to the internet). Supposedly, the first number is the year followed by a letter that's the origin code.

The big pre/post '08 differences seem to be in the VVT - which if you're going to make it go away anyhow, shouldn't play in. I've found a few threads elsewhere on swapping 6.1 short blocks under 5.7 valvetrains of various vintages without much issue. The CR tends to be in the mid 10's depending on actual heads - thicker head gaskets seem to be the go-to for combo's that wind up on the high end.

Might be worthwhile to pop a head off the 5.7 and wander over to the 6.4 and do some mock up? Assuming that's even possible..