I have an SWR workingman 400 watt solid state amp as well. Do you think I'd be better off trying that? I really like the sound of the tube amp though, especially on the highs. I also have a Jazz but I tried that and always go back to the P. I noticed that Phil played a Jazz for a bit there though. Any ideas what strings he was using while playing that one?
I would give this a try. Phil used the preamp out of this amp for a while in the 80s. It's a pretty good sounding amp (I'm not fan of SWR speakers, otoh).
While Phil was using a Jazz, my guess for strings the first time around would be whatever flats were available (ca. mid 60s), second time around, maybe D'Addario half-rounds.
If you really want to go nuts, and be like Phil in terms of increasing the level of high-tech, split the output of your bass so each pickup gets its own amp. Run the lows through the SWR and the highs through the tubes!