'68 Commando Oil filter

Can anyone please advise where the oil filter unit mounts to the frame on a 1968 Commando?

I am guessing it is somewhere under the air filter & forward of the transmission, but can't tell where or what it would attach to.

My filter unit is a cast aluminium with two 7/16" bolts roughly 1 1/4" apart & accepts a Wipac filter.

It attaches to the gearbox cradle which will need 2 holes drilled, someone is bound to have some photos, the factory issued a kit and there is a drawing around, maybe in the later manuals.

See:

http://www.norvilmotorcycle.co.uk/techtalk13.htm

Thank you to both advisors!!

It appears my bike has the Norvil kit, but, considering their location, I never would've found those two holes without direction.
Cheers!
Stephen