Hmm – if I was going to build a 383 and wanted to know for sure that it would be in the 450-500 horsepower range, I’d do the following:

Start with a GM 4 bolt block. I still like the 2 piece seals, but others prefer the one piece rear main – hot tank and make absolutely certain the block is solid – then bead blast the block. All machine work at a competent shop where they will know to use deck plates for the bore and honing. Mains also must be checked and to be sure – I’d ask for an align hone or bore as necessary. Have the machine shop install brass freeze plugs and all new oil galley plugs as well. Buy the best engine bearings (Mahle / Clevite or similar) and have the machine shop install your cam bearings.

Scrub the block and coat inside with Glyptal. Put the block on a good engine stand and paint the outside with the best high temp engine paint Eastwood sells.

New forged steel crankshaft with a 3.750 stroke – don’t go cheap – and new H-Beam connecting rods With ARP bolts and bushed pins. Use new forged pistons from Mahle, KB or other top tier. Have your machinist install the pistons on the rods. Top tier rings (like Hastings) need to be checked and in all likelihood filed to assure perfect fit. All of the rotating assembly needs to be balanced (we’re looking for 450-500 HP here!)

The above is just the short block and to do all this right will be pushing $4-5K. Heads, cam, induction and all the ancillary bits (HEI distributor, Meling oil pump - Milodin pan, water pump, new head studs, timing set, headers, gaskets, etc.) will easily add another $3-4K. (As Pat mentioned, solid cam would be in order so valve train components could be even more.)

In my opinion – done correctly using the services of a competent machinist where necessary and putting the rest together myself - 500 horsepower from a 383 will set you back $7-9,000. Again – my opinion of what it would cost in “my neck of the woods”.

Good Luck,
Glenn