As usual, very nice work! You are definitely inspiring changes in my own restoration efforts. As to how tight, here is the Sil-Pad thermal performance data sheet from Bergquist showing thermal effectiveness vs mounting pressure for it's products. How that translates to how much you tighten the mounting screws. I would assume that you would mount the same as with mica and grease - tight enough to give a reasonable amount of pressure and keeping the hardware from loosening but not so tight as to distort the transistor case. http://www.bergquistcompany.com/pdfs/techLibrary/Sil Pad Overview.pdf I am curious as to which silpad you are using - I was planning on a K10, but looking at those charts there may be some better options from a thermal perspective, though not sure if the difference is meaningful.