If you look at the posted figures for the 2018 model year, a GRJ76 comes in at 4961lbs and the 4Runner is 4400-4900lbs. I think Ben's statement above from an Australian use case is accurate. In Australia, you would expect to see as much as 1000lbs added to it for a well equipped build. More for a deluxe build. So you take a boxy profile with a poor CoD, much heavier running gear, lower overall gears, and more weight...you get a 1GR-FE that is working pretty hard to keep it all rolling. The 1GR-FE is a great powerplant, and it worked fine in almost all situations in my 2004 4Runner, but the 4Runner has far better aero, I never carried that much weight, and if I threw something on the roof or hitched a trailer, MPGs would go to 14-15 and the motor had to rev and downshift all the time.
I think the 1GR-FE in a 76/78 would be over stressed for full time duty. That is where a tuned 1VD is just a flat better option. All that said, here is the states, on paved roads, with out a bunch of stuff on it. It would probably be fine.