Here's the answer on the stock 781 heads. i copied this from another forum, but they don't do much in performance compared to today's alum heads.

The heads now have 2.190 / 1.880 Manley Super Duty Stainless valves, full port work and the valve spring pockets are cut for 1.625 dia springs. The egr ports are filled. The head guy never did fill out a flow chart for the heads, but did say they flow 320 cfm on the intake @ .700 lift and 240 cfm @ .700 lift on the exhaust. About the only thing left to do to them is angle mill them. I've thought of doing it, but I think I'm done with them. I want to upgrade to a set of AFR 335 cfm heads.

Here is the flow charts for stock as cast AFR 325's, you'll note that they flow 384 CFM out of the box @ .700 lift. That's more than Brodix BB2 Extra heads flow fully ported. You can also see the heads cost $2200.00 from Jegs which make that deal even better on the RJ advertisment especially with extra parts.

http://www.jegs.com/p/AFR-Airflow-Re...56123/10002/-1

Zip.

Some blocks will go .125 over===4.375 bore, i just built a 481 that was actually a little too big on the bore 4.377, but it's what the customer had to work with on the budget build.
The problem with the block you mentioned is finding pistons for it. It's not a standard over bore so you may have to have them made (EXPENSIVE) probably over $1000.00.

JMO

Zip.

I agree. After spending most of the day on here researching I can see this is not the ideal block for me.. Right now we do have a basic 454 passenger car block that we will use.... good info and thank you

Re: 496 building advice needed
 

either of the gm heads will work very well. a good 496 can be had very easily and cost effective with the Scat crank and rods with Mahle or Wiseco pistons. a rotator capable of making and handling up to 1000 hp is around 2000.00 with 4340 int/bal crank and good rods w/ 2618 material forgings. as far as keeping the cost down, i would just keep it basic. an engine like this with alky and either heads will make from 700-775 hp. so just use common sense and if you don't have money for heads, use what you have let alone go buy a billet crank and rods! keep it simple and it will do the job.