LT1 heads? If they are iron castings, number 10125320, I might be able to help.
For those castings, the stock valve sizes are 1.94"/1.50". They can easily be replaced with 2.02"/1.60" valves without having to re-harden the seats of the exhaust valves. As long as the machinist is careful in machining the seats, doesn't cut too deeply, and uses a good coolant, teh seats should be induction hardened deeply enough to prevent excessive wear. Mine were. Another good reason to carefully cut the seat depth is to control final installed height. I went for 1.680" to bump the compression higher by shrinking the chamber slightly and allowing me to machine the spring seats into fresh metal on the top side. That also allowed me to use the stock (7.20") push rods with a higher lift cam (smaller base circle).
I measured my chambers at an average of 54.6cc, with very little variation across the sample. The raw runner volumes with plugs installed in place of the rocker studs was 178/59cc intake/exhaust. After valve installation, heavy bowl wor, raising the intake port runners, opening and polishing the exhaust ruuners, matching the gasket flanges, and final trimming, the port volumes measured about an average of 194/80cc, and allowed a much more regular, straight flow to and from the back sides of the valves. I also installed lighter Manley Race-Flo valves with undercut stems to help flow, and radiused the front faces of the valves around the margin instead of a multi-angle valve job, since I wanted better durability for a street-driven engine.
Coupled with an adjustment in intake port height and size, a different cam (twice), real springs and rockers, screwed studs, and a little tuning, the head changes really woke of the otherwise docile "260HP" Impala engine.
