I know that Namrick don't do Grade 8 (at least, not on their website). I use Margnor for those that I care about, like the front suspension. To be honest, I wouldn't be too worried about them for the mount. My fastener pack (2003) came with capheads and so that's what I've always used. I don't know why, but in that situation where it goes into the mount tube a caphead just seems more appropriate, not sure why. I understand what you mean on the length and would also want to double check. Is the mount slightly more than 2in, as with no washer you should have at least 12mm showing? I just looked at the packs that Caterham are currently selling for imperial, and they are 1/2" x 2.5".