I wouldn't take any of my cars to Jiffy Lube if my life depended on it. I have a co-worker friend who brought her Saturn there a few years back and they did not tighten the drain plug. A few miles down the road the plug worked it's way out, the oil drained out, and the motor seized. She had to fight with them for weeks to get them to pay for a new motor for that car.
I'd also recommend staying away from synthetics for these motors, traditional oils will work just fine. I've recently made the switch to using diesel oil, Chevron Delo to be exact, on the recommendation of my LBC mechanic friend. He claims that the diesel oils provide more stable oil pressure numbers as the motor gets hot. Cars that he's worked on that have the pressure fall way off when they get fully hot can maintain higher numbers using these oils. Plus I've read some info on the zinc additives that most diesel oils still carry in them that is beneficial to flat tappet motors. These additives have been removed over the years for the most part from gas engine oils in the name of lowered emissions and advances in engine design, and are slowly being removed from newer diesel oils also. There was a good article on all this some time ago, can't remember where I read it. If I find it I'll post a link. If I remember correctly you want the oils that still have the older CI-4 or CI-4+ rating on the label, not the newer CJ-4 rating. The newer CJ formulations have little or no zinc additivies in them either, such as the current Mobil Delvac 1300 super and Chevron Delo 400 LE (low emission). I've found the older CI-4+ Delo formulation still around on the shelf at Pep Boys and Wal Mart for around $10/gallon, as well as Shell Rotella with this rating. I've just changed my oil this weekend to the Delo and I haven't driven the car yet so I don't have any initial impressions.