I used to own a vk 60. (now a vk75SE) I can't specifically answer your detailed question. I can say the front two input tubes (the 6sn7's alone vs in the row of 6) are by far the most critical and will give you 70-80% of the sound change vs changing all 8 6sn7's.
Try expirimenting with those front 2 input tubes at first. I liked the RCA 5691's.
Also, when the amp is cool, pull the tubes, clean the contacts, sand the tube pins with 400-600 grit paper, clean the tubes pins, and reinsert. Nice performance gain for next to no $$'s.
Good luck, that's a GREAT amp !
Try expirimenting with those front 2 input tubes at first. I liked the RCA 5691's.
Also, when the amp is cool, pull the tubes, clean the contacts, sand the tube pins with 400-600 grit paper, clean the tubes pins, and reinsert. Nice performance gain for next to no $$'s.
Good luck, that's a GREAT amp !