They are surprisingly ok on the road, but definitely not fast. Even slight uphill grades or headwind slow a BJ60 down. If there are mountain passes around expect to be churning along in third gear doing maybe 70kph. But they are economical to run and have a proven track record for longevity. I plan a turbo for my 3B soon but even as it is, it isn't that bad.
If you are realistic about your goals repowering an FJ60 with a cheap, low mileage, rusty BJ60 donor is the most likely swap to pay itself back quickly (around here anyways). It will not make the truck 'better' for driveability on the highway though IMHO. A good 2F still has more torque, runs smoother, but it costs twice as much in fuel to get where your going.
If you are realistic about your goals repowering an FJ60 with a cheap, low mileage, rusty BJ60 donor is the most likely swap to pay itself back quickly (around here anyways). It will not make the truck 'better' for driveability on the highway though IMHO. A good 2F still has more torque, runs smoother, but it costs twice as much in fuel to get where your going.