For all intents & purposes, doing rings is a big job. I mean compared to doing a head gasket w/ lifter R&R. 257K means your ZJ has alot of "experience", so I'd def do a timing chain since you have the head off. If you're gonna do this job yourself, just make sure you get an aftermarket "coated" gasket, like FelPro part# 530SD. The dealer gasket is multi-layer steel, uncoated, and is intended for a new engine with no surface imperfections.
You'll also find alot of use with an air- or corded-electric-power drill fitted with a "cookie", or surface prep disc, they're not to much at the autoparts store, and you'll like using it to clean and prep your deck surfaces. 3M calls them "Roloc" discs, and you'd want to use the grey or green ones, trust me, it saves ALOT of work. Of course, a repair manual and torque wrench are ABSOLUTELY necessary. At 257k, there's no reason you can't just "freshen up" the top end w/o doing any bottom end work, even w/ some slap when she's cold... I'm done rambling now...
1994 ZJ, 5.2L/46RH, NP242 & D44HD Swap, 4" SA Lift, 31" KM2s, and all the usual... I only lifted it so I wouldn't have to drive my grandma to church anymore... ;)
Remember: Every time you call a Jeep a "car", God kills a kitten.
Red Jeep Club #657