I use Castrol GTX and have always heard good stuff about it. For a filter, try to use Purolater, Wix, or AC Delco. Avoid the cheap Wal-mart type brands like Fram and Pennzoil. There's nothing wrong with 10W-40, that's what would have been specified when new. Regarding additives, I don't know. Do be careful with products that promise to loosen up/clean the inside of the engine, because with your mileage, there could be a lot of junk in there and it will clog the oil pickup screen if it is knocked loose into circulation.
Currently an '86 CJ-7 and a '77 CJ-7 Golden Eagle---#4 and 5 following a '01 Sahara, '90 Sahara, and '85 CJ-7....