5.7 heads on a 6.4 short block?

Here's a good guide:
5.7, 6.1, 6.4 Hemi interchange selection guide

Sounds like if you can find donor apache front cover and a VVT delete cam drive (is the original cam drive system there in the 6.4?), you could be in business. There seem to be a few on ebay for $85+
I'm assuming accessory drive would be a 'custom' affair anyway?

The older non MDS, non VVT lifters seem to be compatible with the 6.4L shortblock. Pushrods I haven't seen any info on but seem to be pretty easy to address.
The cam would have to be compatible with a VVT shortblock, but again assuming custom/aftermarket here anyway.

So it seems the oil pan, intake, heads (and covers, fuel rails, etc) and lifters will swap. The front cover, cam, cam drive, and many accessory parts probably won't. The compression will likely be down compared to a stock 6.4L, and choices for intakes will be a little limited and you may need to grind clearance in the block or use a spacer to raise some intake manifolds. It should still run like mad.

The rest is just a matter of getting the electronics to fire it off.

I'm no authority on the subject, but luckily there seems to be a lot of good info out there.

Looks like there's kits out there to use the early cams in late motors.