i am not sure if parts are hard to find for those tercel wagons. i would think lots of parts interchange from a normal tercel or other toyota vehicles.
you could also look for one of those cool toyota vans from the 80s/90s like this. they came with optional 4x4, like the tercel wagons did. not sure if hte van got in the 30s but a friend had one when i was in high school in socal and we fit about 15 people squished into it so it would fit your space needs.
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or a toyota previa. my mom had one and this was a super dependable van with tons of room. still didn't get hte 30mpg though.
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i think mazda made a small van/wagon called an mpv that probably got good mileage and was tall enough. yup, google says mazda did make it and it could be had in 4x4 too
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i knew that is what another buddy had. his was 4x4 also and we would take it to carry our surfboards for out of town surf trips when i moved to texas. my 85 f150 didn't get great gas mileage so