dave replied:

Comfort...

That's the real difference.

The 75 series has leaf springs all round, the 78 has coils up front and longer leaves at the back.

Other differences of note..

The 78 has bigger brakes (and 5 stud wheels)
The 78 has digital odometer (these really bug me when filling in log books)

I'm not sure about the motors, I believe that the Turbo model in the 78 is a purpose constructed engine rather than a bolt on job.

Me. I've got an 88 model 75 series, and freqeuntly use hire troopies for work, The level of comfort of the 78s is poles apart from the 75s.

Now, without trying to take you away from this excellent site......
there is a Troopy group out there at.

groups.yahoo.com/group/troopyoz/

BTW, you'll find exploroz listed in the links section of the Troopyoz group.

Dave

andy replied:

Toyota have a run out sale on the 78 series. Maybe there is a new model just around the corner.