I thought some early 601s needed valve adjustments.

If there is some shank above the head surface but vice grips don't do it, something like this -

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96335

or this -

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94640

might do it.

The bolt takes a 10mm wrench but it's otherwise known as a 6mm bolt. You should be able to find a suitable metric bolt at any hardware or auto parts store. Bring a good one to match.

The torque is so inconsequentially low that you should use a screwdriver type tool rather than a wrench. If it's leaking, you need a new gasket, not tighter bolts.

Sixto
87 300D