Quicksilver V4 , change the 12FQ7 for a 6CG7

I've read that you can make a modification on the Quicksilvers V4, it would be posible to replace the out of production 12FQ7 and put a 6CG7 or 6FQ7 instead... can someone explain??? Thank you
Why don't you just call Mike at Quicksilver and ask him? He would be the one to ask.