The 330K resistors are the Grid return resistors. R-117-118-119-120. Change them to 220K or 200K and then change the coupling caps to whatever the metalbone kits sent you. Probably .1uf. The screen resistors(100ohm) are an add on to alleviate or at worst minimize arcing of the tubes. It's more prevalent on the Russian tubes BUT it's a good idea on all tubes. Go into the Stickies Subforum and find the Thread "Common FISHER PARTS". There is a post on the 3rd or 4th page IIRC with pics on how to add them on 7591 sockets and also the 7868 sockets.