Thing is those are not stock heads they are SMOG heads.
You could swim in the combustion chambers they are so big ( 76 cc ).
With flat tops your compression will at best maybe 8.5 to 1 if that high.
Compression builds power, your gonna want at least 9 to 1 to make any decent power numbers 10.5 to 1 would be better. Look at any muscle car era engine data numbers and the power numbers always went up with the compression.
Not saying you cant make good power with those heads I.E. bowl blending, port matching, cutting for bigger valves, three angle vavle job etc, etc, etc.
But for the money doing the above mentioned to some vortec heads ( 64 cc ) would pay off in much bigger dividends. The compression ratio with vortec's and flat tops will be right 10 to 1 which means you'll have to run 03 octane gas but your Hp number just went up significantly no other change will yeild you more power than that. Most junk yards will pratically give them to you and then take them to the machine and for under a couple hundred bucks you have some very good heads.
But either route your gonna have a decent running 350.
Hell I've seen people take a bone stock 350 slap a four barrel intake, carb and a small flat tappet cam, cram a 411 out back weld up the spider gears, slicks and WAM BAM they have a drag car and have it run like a rapped ape but with a little more investment, time effort you can really have a barn stormer.
Goodluck and Happy Thanksgiving, Charles