When I rebuilt the transmission for my D250 Cummins, the trans cooling lines were rusted to the point of breakage. And they are 1/2 od !!!. Not available from the dealer anymore. So I bought a coil of 1/2 copper and flared and bent them into position myself. No leaks yet in a year and a half. In my case, they travel pretty far from the radiator before they are clamped tight to the trans.
Coiled is 'soft' copper. It will flex, but not really intend for repeat movement. also, trans lines are closer to the mounts, so less movement. Still might be ok. I'd suggest leaving a loop in it, but he's trying to minimize...