Pentax 67 outer bayonet extension tubes - DIY

Hi guys,

I am after the OUTER bayonet extension tube for the Pentax 67 system however they are quite rare to find...at the point that I am considering to make them by myself.
Since they don't have any glass, making them from scratch should not be difficult, however I will need some drawings. Do someone out there has any technical drawing of the Pentax 67 bayonet mount or something which may be useful to make an attempt?

Cheers,
Ferru