If it was me, I'd ditch the factory hard lines, go with -6 hose all the way. You're gonna beat that car for 24 hours and don't want a cooler line to crack. The hose is the least expensive part of AN lines anyway, and if you run it all the way you eliminate fittings and adapters as potential failure points.

Just for God's sake don't jam NPT fittings in the trans. They're inverted flare, most likely 5/8-18 thread.
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1988 CVLX Formal Roof (Love Boat) POTM July 2019 & Aug 2020, 56K
E-code lights w/ relays, LEDs w/ switchbacks, 15x8 Ansen slots w/ 255/60 BFG's, Kenwood stereo, various hacks.