Captainr6

I need help deciding what way to go. I dont know much about the 5.3l heads except that they bolt up and raise my compression. i cant seem to find any spec #'s or a post. Im curious if i should buy the 5.3l heads and if my spings and rockers and everything will fit in it or if i port/polish/mill my ls1 head if that would be better. Plus whats a safe compression on these motors? 140,xxx miles on her. bone stock. I plan on doing head work, lt and spark plugs right now.

so, 5.3l head or port/polish/mill my stock ls1 heads.
i know stock we go 10.1.1 - 10.5.1 if im not mistaken. but if i do mill my stock heads, how much can i drop it to be safe.

if you guys could give me some good feedback id really appreciate it.