It is true that the later type has the upper port attached to the
front brakes. My mistake, I forgot that there was a later master
cylinder and didn't look it up in the Haynes supplement. Obviously,
you should hook it up as the manufacturer recommends. North America
and the BenLux countries had a twin circuit master cylinder from
1972-78 so we still tend to use the older type.

The only explanation for this that I can imagine is that the later
type master must have the two piston solidly connected or only has one
piston for both circuits. That's my hope anyway. I know I've seen and
exploded view of that master cylinder somewhere but I can't find it
right now.

If you are putting on a brand new master cylinder it is a good idea to
bench bleed it first. I have some connectors and brake line from an
old car and connect this to the appropriate connectors on the master
cylinders. Put some clear tubing on the stub ends of the brake line
and route it into the fluid reservoir. Fill the reservoir and push the
push rod up and down with the cylinder held vertically. One good way
is to put the pushrod in a vise and push the cylinder up and down.
Keep doing this until there are no more air bubbles.

This really helps with the feel of the pedal. The last one I did was
rock solid but it was a straight swap so I managed to not introduce
any air into the old lines.

Cheers,

Kelley