Cooler line size

I'm considering doing a conversion from a 727 to an a500. The Mopar OD transmissions have 3/8 cooler lines, where the 3 speed tranny's are 5/16. The fittings in the radiator are still only 1/8 NPT.
Do I retain the 5/16 lines and just adapt up at the trans, or do I bend up 3/8" lines that would directly screw into the OD trans fittings, and then just adapt at the radiator, or do I have to get a radiator from something else that also have the larger fittings/ so as to not have a restriction to flow? I do plan on using both the included trans cooler in the radiator and an auxiliary cooler out side the radiator besides.
I know that many a500/518 failures are fluid overheat problems in the first place, so I don't want to handicap that flow with too small of lines. The"victim" of the proposed swap is an 85 D150.
The other option I have on hand is an 833od conversion which would make it all moot... The debate on which way to go/ whether to stay auto or swap to a stick, is subject of a different thread.....