What's the biggest duration/lift for both intake and exhaust that I can get away with without having to fly cut?
I have an Lq9(Flat tops) and SDPC CNC'd LS3 heads milled down to 66cc with Manley valves. I plan on using a stock 6.0/6.2 head gasket and eBay head studs(<-- had good luck with those)

 

check with comp on their thumper series.

 

if i recall Pat G mentioned i was bored line at 235/239 621 lift, this is why you'll see alot of setups close to this spec on cam

 

Those are designed more for sound then performance gains. Yes they give gains but not like LSL or XER lobe patterns.