I just bought a complete eagle 109,000 miles, non mds engine off CL for $300 threw it in my truck and am driving it now. That is a screaming deal but I frequently see cores around $500 and have 2 sitting under the bench right now. I more commony find the early ones for under $500 and have 3 of them sitting around. While it will not get you 700 HP (probably be close with some cubes and compression thrown in the short block with a good $500 arrow intake) a new 6.4 cam (.577 lift) from the dealer cost me $68 and matching valve springs are under $200. If thats not enough regrind it for under $100 to get you what you need. The factory lifters in that core usually will work in a 700 hp motor, stock 440 ones not so much and the cheap regrind only gets you a flat tappet cam. Another thing about the new hemi, real nice, MLS head gaskets are $22 from autozone.

Really though I don't see a reason to build your own stroker gen III when you cna buy a 6.4 short block from the dealer for around $2500 or in other words the price of a 6.4 stroker kit for your 5.7. Mill your boneyard heads for a little comp, do a little port clean up, throw on a good intake and you probably can be under $4000 in a quality motor then the exterior stuff is very similar price like quality headers.

Another option is buy a complete used 6.4 off car part . com or ebay throw in a bigger cam, better intake and quality headers and you can be close to 700 at the flywheel without even pulling the heads. After all they are making nearly 500 SAE net with sucky exhaust and emmision friendly tune and cam and a quietified intake.