Ok got ya. Yeah but should be around 500 if built well. Usally when people go to the effort of buying gm performance products heads they usally have a good idea of how the rest of the build should go. If it was built by clowns it would not have those heads so sounds like a good engine.
If i had a parts list i could come up with a price. As far as sbc for a bracket car that is a perfect setup. I would bet someone spent more than a few bucks to have it built.
In the sbc world blocks are a dime a dozen so are parts to build them up. Mild builds can be very inexpensive. What you have sounds like a nice little gem. It would be a shame to pull it apart. But sbc are much less forgiving than big blocks.
Here is a dcr calculator problem is i dont think any amount of cam is going to let you run 13:1 on the street and use iron heads. But i have seen someone pull off 12.5:1 on the street but it was a fair weather car. Now the right cam and a few gallons of 104 octane per tank full you might make it work with careful tuning.
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Fyi i got a feeling from this post that you got a few bucks to spend on the right stuff. The LS motor is awesome for street cars. Price is a lot more than a gen I. But many ppl have them over 800 hp with turbos and mostly stock engines. Even with the 5.3 will make a butt load of power with simple setups. The 6.0 from an escalade is good for 300 hp In stock trim. A cam and some exhuast work 350-400 is not hard to find. It is a lot more work to install but work dam well and will last 100k miles no sweat. Also makes for a very smooth and fast car. Only reason most ppl dont upgrade is cost. The heads and block are a leap forward in tech. The stock big valve LS heads flow better than some aftermarket heads for the gen I.
Sorry for the long post hope at least some of the info is helpful.