i have a Jazz pup in the neck of my Jackson SLS and i really like it. the SLS is flame topped maple over mahogany - the RG1570 is basswood - i'm not sure what that may change exactly, but i know it will be different.
i haven't tried a Fred in the bridge but have tried it in the neck of an RG and it was o.k. - not as tight and defined as i would prefer but i also was limited on what i tried it thru - Boss Micro Cube, so i wasn't expecting much. the Evo pup in the bridge of that same guitar didn't feel like the Evo i put in my
alder bodied strat - so again, i'm not sure how the tone on the basswood will sound. i believe the JS1000 is basswood and that is what is installed in there - so i would guess it is what Joe is using. the nice thing about pups is if you don't like them you can change them.