Clean the engine with something like Engine Brite, they make a foamy spray that sits on the grease for a while and cuts it really good. Comes out spiffy. Sandwich bags and masking tape works good to cover electric parts, and use a gentle spray to rinse it. And be aware of what's under you, it makes a big oily mess, very environmentally unfriendly. But yeah it does the job well.
I use synthetic 10w40 in my '93 4.0 with 200k. The pressure creeps a little low when it's hot, nothing to worry about but I might try out 20w50 next time. The engine purrs like a kitten though. My oil still looks perfectly clean after 3,000 miles. The PO had been running synthetic only for a long time and it shows.
I also add a 4oz bottle of zinc phosphate additive every oil change. Anybody with an older vehicle should be aware, and most people aren't, that ZDDP was in all engine oils, and been phased out in the recent years. Pretty much all engines now use roller lifters and rockers which are fine without it... ours use old style flat tappets that will will wear themselves and the cam lobes out waaay faster without the zinc. Apparently it can be harmful to your cat, which is why it was removed. I'd rather look out for my engine than worry about the cat, which isn't monitored by the ECM, and in NY we don't test emissions on pre-1996 any more.