All my Newells have graphite spools and P-series frames. Most reels can be swapped, but you usually need to fool around with the bearing shims to get the spool centered and have the correct spool-to-frame clearance. Can be frustrating. Some spool/frame combos just don't work because the tolerances stack the wrong way, but you just have to find out by trial and error. I think there was an early vintage of P-series that had a different spindle length that won't work with a graphite spool, but some of the old Ps and all of the new ones can be made to work.
I sold the S-series frames with the P-series spools on ebay and got similar prices for what a plain S-series goes for, so buying an old S-series and then selling it is an option to get a graphite spool more or less for free.
I told you. Just sell the"P"'s, and buy some old school "G"s. It ain't worth all the trouble. I've been fishing with some of the first "G"s since I got them from Carl when they first came out. I wouldn't give them up for anything else.