just wondering about what a couple different pistons would place me roughly compression-wise on a stock deck height non milled heads 355 lt1

+5.00cc flat tops with 2 valve reliefs
-4.00cc domed with 2 valve reliefs

also what's the average compression ratio you'd recommend on a daily driven lt1 with some nitrous here and there? (not often if at all most likely)

 

You do not want a domed piston, not sure what the compression will be, but with -3.00 cc dome my compression was way over 13:1, that was with heads milled .005 or so, block decked etc (forget actrual numbers). Most will agree to go with a flat top. For a compression I would maybe look at what the cam recommends. 11:1 is quite safe for a street car. I personally went higher (12:1) but 11:1 should do you fine, and leave you quite a bit of safe zone.

Also, nitrous does not mind compression.

 

There are a million CR calculators on the web, including on this site. As far as what CR you want, depends on the fuel used and the cam. In general, a small cam will want ~10.5:1 and`a big cam maybe as high as 11.5:1.