Hi Krow
Thanks for your enquiry regarding Penn 50W reels, firstly the Penn 50TW is a single speed model with One drag fibre washer and the Penn 50 SW is a Two speed model with Twin drag fibre washers, so normally I would recommend using the two speed Penn 50 Sw reel with twin drag washers which is more than capable of using 80lb braid on without shortening its life. yes the 50 size was originally designed as a 50lb line weight reel, however more than capable of working well with 80lb line ( braid or mono).
The thrust washers you have mentioned are called Belville washers, these are a constant pressure spring washer which applies pressure to the drag washers, they come in a variety of thickness to suit required drag working range, firstly I would recommend having your reel Blueprinted to start with then we can set up the required drag range and pressure to suit your application, it is imperitive to start with flat smooth drag metal plates and then drag fibre washers in good condition before you do any tuning work changing Belville washers.
FYI : My solo Swordfish recently was caught on a Blueprinted Penn 50 VSW using 80lb JB hollow braid & 37kg mono top shot delivering up to 20KG (44lb) of smooth consistent drag pressure for nearly hours with no issues, the Penn 50W reels are highly underated, IMHO.

cheers swordfishsteve
REEL REPAIR GUY - Swordfishsteve, That Is Who I Am and That is What I Do : See More At :www.reelrepairguy.co.nz