Just wondering which parts from the 6/0 will also work in the 9/0?
A lot - check Mystic parts and look at the schematics: Gears, screws, drags, collar, clamp, handle, nuts, bearings, lugs, springs are. Mainly check bridge, yolk, jack. I did a while back but have forgotten. Eccentric lever is different.
The main difference is the pinion gear. The Sleeve and Main gear are interchangeable.
Does it use the same bridge or does a 9/0 have a larger bridge?
115 9/0 bridge is different.
do the 6/0 and 9/0 use the same drag washer kit. i want to convert an old 9/0 from 3 to 5 washer. its the type where you can get to the washers from under the handle without gutting the reel
I believe they use the same main gear so it should work fine. Might be a chore getting the drag washers out though
I find it fascinating to get one of the old Penn catalogues that came with their reels and read across the parts between different reels. So many screws are used in different places in different reels, for example. Makes sense.
When it comes to the 9/0 and 6/0, don't forget the red plate H version of the 6/0 as that had more parts in common with the 9/0 I believe.