I had a 68 for a while and would like to change oil as I have no idea when it was changed last time.
As far as I can see, the cross member with trans mount must be removed so oil pan wan be opened. Am I right?
While in the guts, what should be checked?

 

Make sure linkage works and kickdown cable is connected and resistance is felt on the last 1/4 inch of travel.
Ensure vacuum modulator has no holes in diaphragm when sucking on hose.

 

Where can I found an exploded view of those parts or a manual page(s)?

 

Get a Motors and or Chiltons manual for your car .It can help you in other projects as well.Good luck to you.

 

Are you sure the trans is original? If you know the model of the trans finding info on it will be easier to find. Some gear boxes need removed and stood on end to drain. I do not remember a "pan" on any gear box. Some do have drain plugs. Wait, are you calling an automatic trans a gear box?

 

I think this is the "case" Gorn.

 

This threw me off at first too. FYI to the O.P., a "gearbox" refers to the steering box.

 

Well I guess a box filled with gears might well be a gear box. Whether it's clutch or automatically operated via a torque converter (I guess) do not change its gearbox condition.
And here is a picture of what I guess is an oil pan.
Ths leaves open my original question how do we change oil there?

 

 

You remove all the bolts around it. Pry it loose. Dump the transmission fluid out. While you are there change the filter. Get a new gasket. It probably came with the filter. Put in new transmission fluid. I don't remember offhand how much you put back in when changing the filter.