its going to be a bitch to take the piston out from underneath unless you take the gearbox off, take the main crank seal housing, oil pump, oil squirters etc etc and drop the crank.
it will probably be easier to take the head off and just replace the rings and slap it back together if you want to do it on the cheap, but you might as well do the main and big end bearings while its all stripped (it'll only cost you around $140 extra for ACL bearings if you're doing it yourself).
you'll need to check the clearances of the bearings and the bores too, and figure out why only #5 lost compression.