Hi M,
I think the operative word here is possible. You can use a pentode as the first tube. If you’re set on it but I might start with something like a 12by7 or ecc88(or is it 86?) or 6sj7 in octal. In any case none will work in your board, at least without a bit of redesign. What triodes do you have on hand?As to the second part. I will post a schematic soon, easier than trying to write about it…John