anybody know what size the oil cooler fittings are in the radiator? thanks

they look like standard 1/2" pipe to me, I do not however know.

My 86 J code 6.2 in an M-1009 has 5/16" inverted flare fittings for the transmission cooler lines. The engine oil cooler lines had a 3/4"-18 thread that sealed with an o-ring. I never could find a suitable adapter. My 2002 G-van with an F-code 6.5 had the dreaded snap ring fittings in small for the transmission cooler lines and large for the engine oil cooler lines. When i unscrewed the transmission lines, i found that the radiator had inverted flares. 5/8"-18 is the thread size. It is standard 3/8" steel tube. The Earl's Plumbing adapter is 991947erl, this gets you to a dash 6 AN. The transmission end is the problem, but search around, there are adapters being made that plug into the snap ring fittings and give you a dash 6 male end to work from. If you use NEW snaprings and NEW o-rings in the fitting and SECURE the hose so line pressure can't push the adapter out of the fitting in the event of a snap ring failure, it should be a safe solution.The engine oil cooler adapters unscrewed to leave a 1/2" NPT female in the radiator. Very easy to adapt to most anything. Beware, GM seemed to use different stuff at different times. Your results may be different from mine. Hope this helped.