How thin of a gasket will I need then? If I mille .040 and go with we'll say a .020 gasket, what will it be at?

 

Mill .040 and run a .040" gasket and you should be 10.5-10.6 cr.

 

Will this work in my situation also??

putting 243s on a 5.3??

How thick is the stock replacement gasket??

 

Yep, but you wil be closer to 10:1 because the stock 5.3 heads have small chambers to begin with (61 I believe). The LS6 chmabers are 64-65 so You would not gain as much compression as the 6.0l guys. Now you can mill your 5.3 heads .040" and run a .040" gasket, and you would be somewhere around 10.5. The stock gasket is about .054".

 

Where or who could I get a .040 gasket from for a 5.3??

 

Not sure, but Cometic may make one, Fel-pro may as well.

 

You might want to check and see how much the pistons are sticking up out of the hole. All the LQ4's and LQ9's I have worked on were .008" to .012" up. You would not want a head gasket too thin, .035" quench is the minium I would suggest.

piston up measurement + .035" minium quench= head gasket thickness