pentax 67 extension tubes

who can give good advice on the extension tubes and metering for my 67 ?

do i simply change to manual on the main lens, then switch back to auto before snapping?

Do the 67 tubes have electrical contacts? I know my 645 and its set of tubes have electrical contacts and therefore maintains full auto aperture TTL metering...

Yes, there's light fall-off but the camera works it all out for you unless using a handheld.

I'm not familiar with the 67 but does it have a different effect regarding metering depending on what flavour of 67 you're using? 6x7, 67 or 67II?

Will

There are NO electrical contacts on the tube set: that has caused a lot of trouble when I tried TTL metering with my mark II body; they work properly only on stop-down metering as I found vast under-exposure when I relied on the Mk II metering with lens at open aperture.
With the earlier body I have ca 1977 I give the extra exposure needed manually.

thanks everyone

the drinks are on me

Knowing the proclivities of some of the folks around here, that could turn out to be quite expensive!