Terry,  I think you would find it very difficult if not impossiblr to
use PVC pipes.

The pipes have numerous bends to route them t hrough the chassis
crossmembers.

I think you could do it with copper if you remove the old ones in one
piece so you can duplicate the bends.

I do not know if copper is compatible with the other metals in contact
with the coolant solution.

Perhaps a chemist on the list can address this issue.

Good luck.

Harry Patrick