Hi All!
I couldn't help but notice the statement by the OP:

We checked the IP tang alingment when I thought I had the cam out of phase - it shows up around 14 degrees ATDC. The cam was out of phase by 180 degrees, but that got fixed.

Does a 603 really run IP timing at 14 degrees After Top Dead Center? I'm not an expert on 603s, but if it does run 14 deg after TDC, its the first engine I've EVER run across that does. Have you actually set the IP start of delivery timing?

If the IP timing is supposed to be 14 deg Before TDC, that would explain the total lack of power.
I reserve the right to be wrong. But I just thought maybe I could help...
Cheers!
Chris