If that is not in the budget, I think with a set of 906 heads ($600 from indy all built and ready to install), a set of pistons close enough to stock weight that you dont have to get the rotating assembly balance 10.8+ to 1 compression, and a stout flat tappet cam, will get you plenty of power, cost would probably be around half of the cost of the above engine...
Those Indy heads are a waste of money ... you can get the same low end rebuild at the local autoparts store ...
Open chamber heads AND 10.8 compression is not sound advice, to get that much compression with an open chamber head will require a domed piston ... or cutting a lot off the heads ... I think the only dome available now for a 383 is a KB and it will require a rebalance.
The OP needs to state his budget and desires of how the engine is going to be used, 425HP is doable but hard with stock type parts and/or be pump gas friendly.
Sorry, that is a typo I meant 9.8 to 1, if you see earlier in my post i said "sub 10 to 1".
I had some good luck with the indy 906's, and a friend of mine used a few sets over the years and they are still together making good power, we redid the valve job but besides that they are OK for the money, the reason I like them is cost, if you buy a set of heads, send them to get cleaned, and checked, then buy all the parts, you are going to be over the cost of them heads all assembled..
I was just giving a cheap alternative to what I said I would be looking to accomplish...
