What about a take-out/low mile 6.4 apache (about 4k) has factory steel crank and awesome cylinder heads that you could make even better- 392CID
Drop in rods and pistons-$1500 (13 or 14 to 1 comp)
Lock-out the cam phaser-$100 bucks from comp
Custom cam-$700ish
total 6300

Fuel Delivery Options
1) Dominator carb: 1200cfm or whatever - aprox $1200
Ritter Dominator intake $700
MSD6 G3 hemi ignition and harness $740
total $2640

2) Holley EFI system: approximately $2600 - $2800 - ball park. Rich/fastman efi might have a more accurate number.

Figure 1.5 to 1.6 HP/CID = 588 to 627HP - maybe more?

This motor may be around 75-100lbs lighter than a big block and still lighter than a small block.

This would be around 9kish total...Numbers may vary a little bit, but you get the general idea