I'd pick the MPV. More space, same engine as the Ranger/B-Series. Engine parts should be easy to find, thus... but I don't know about cosmetics (lights, trim pieces, etcetera).

The Carnival is a car-based minivan. Smaller. Not quite sure about the reliability of that year of Carnival. Should ride better... but other than that, I'd go for the truck.

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Why buy a converted RHD MPV when you can buy a local one for a good price with less hassle and headaches over the conversion? Living with a single sliding door... on the wrong side of the car... is an awfully big sacrifice to make (in terms of convenience and safety) for whatever savings it gets you.