If you're good at bending tube, try the trans cooler hard lines at auto parts stores.
On racecars & hot street cars where originality isn't a concern, I often mount them vertically (inlet & outlet @ bottom) off the face of the radiator support using Adel clamps.
Between anything that vibrates or moves even slightly and hard lines, a short rubber hose is a good idea. If you're plumbing it into the existing hard lines at the radiator, you can do it with fittings & hard line. Might have to spend a little time with a Dorman (or similar) catalog to find the fittings you want.