well i am plaing to do a LS build and want it to know if this sounds good or not... i am plaing to clean up my head but keep it stock to when i get more money but do you think my head will hold with pr3 pistons and what will be the CP also will i have to run higher grade gas?

you can run high gas no matter what. but to HAVE to run higher octane gas you will need a 10:1 compression. The pr3's will give you that. You can fit them on stock rods as well. The head will hold it but would really want some new cams to make use of the compression.

so how much hp am i looking at? also im not trying to run 91 because its alot over here in cali.

If you don't want to go to a higher octane then don't do the pistons. The compression needs the detonation of the higher octane. You will probably knock and ping a lot running 87. If you are set on lower grade gas then do your head and not the block. throw in some 403 cams, valve springs, and tune it. maybe an intake manifold and throttle body combo. That should bring you to around 145whp.