Will 99 ls1 heads fit a 2000 without mods? and if there milled 30 thousands what would the compression be with stock gaskets.Are 2.05 valves a good size?

 

Yes.

Around 11:1 ?

Depends on the application. You'll have piston to valve clearance issues with a big valve like that and a milled head.

If you don't have an aftermarket cam already, there's no point in switching heads.

 

I plan on useing the cheater cam with those heads,with do I have to do to make them work on the stock shortblock?

 

You shouldn't have any PTV problems with a small cam like the Cheater, but check to be safe if you're going with milled heads, a 2.055 valve and stock pistons. Worst case = flycut the pistons.