easiest to pull the engine out of the top.
the stock pistons are fine so long as they arent already chipped. the stock pistons take a lot of abuse so long as youre not just throwing things at it so it blows up. you need to keep the car tuned well.
if the engine is already out i would put a cam in it. with any cam you can EASILY run lower 13s if not 12s.
if youre getting head work done i would look into a bigger cam, but that will also require bigger valve springs and more than likely a timing chain upgrade (which most people are scared of nowadays with all the stories of them breaking).
the best tuning source for these cars is HPTuners.
how fast do you want to go with it? for 13s you dont even need a cam or head works, so what are you really after here?
