I had a 79 FJ40 before I got my XJ. I had the stock I6 & 4 speed. It was slower than sin, but nevertheless really fun to drive on account of excess low end torque.
I was building it with my sights set on the Hammers, but at some point during the build I realized it was just too heavy & too dated for really tough trails.
The toughest trail I took it on was the Rubicon, & while I didn't really have any trouble, it sure was a lot easier when I returned 2 years later in my XJ. If I were only running moderately difficult trails like the Rubicon, I'd probably sale my XJ & get another FJ40.
One good thing about FJ's is that they appreciate. I bought mine for $4,000 & sold it 5 years later for $7,500.
Paul