Renago I must politely say I am fairly sure you are incorrect. Many 75/78 parts are interchangeable true, but I just don't see where this extra length is. My flatmate owns a 75, and I own a fte 78, so just walked outside to check and they are the same.
Regardless
@cannedcruiser, I would encourage you to keep looking in Australia, for both 78 and 79 rigs with the fte motor. They were an expensive option, and the community here takes maintenance and tidiness pretty seriously. Though many rigs have high km, you have to remember that we have no salt on our roads, and most of the driving is flat endless highway. I bought one with 400000, and have kept up the regular maintenance while putting on another 50000, so far the only extra work has been reco'ing the xfer case and prop shaft uni joints. I've done other things but not out of necessity.
Another bonus of buying from Aus is that you often get many quality aftermarket additions like bar work, long range tanks, lockers, lifts, pop tops, interior consoles, drawers, kitchens, uhf radios etc etc.
I am familiar with your driving conditions as I grew up in Victoria until 13, when my family and I began travelling before ending up in NZ. After some stints back on the Island as a young man, I eventually immigrated to Australia. I would certainly have a hard time buying a BC vehicle with more than 200000km, but down here it's a bit of a different story. As with every vehicle a thorough service history is worth it's weight in gold when buying 2nd hand.
Good luck with the hunt! If you end up finding anything in the Perth region, I'd be happy to check it out on your behalf, and have an excellent mechanic here who can assist as well.
PM me if you like, who knows we might know each other from the past even haha!