I need to connect the supply and return lines of a Char-Lynn 2000 series motor with 5/8 and 1/2 in manifold ports. Is there a way to do that?

You need to remove the back plate which is "manifold mount" and put on a standard back plate with #10 SAE threaded staggered ports. You cannot thread any fitting into the manifold ports and there is not a manifold adapter which will allow you to connect the hoses without crossport relief.

The back plate is 21564-001. Your cost is 158.95$ (8/26/11).
You will also need a seal kit which is 48.78$ (8/26/11).