I took a look at the frame dimension diagrams in my '88 FSM. Turns out there are more differences than I thought.
As long as you have a SWB truck frame (RN61 series, reg cab & short bed), then the length is the same, same wheelbase. The first 2 pairs of body mounts are the same, but things go differently from there.
A 4Runner has 10 body mount points, a pickup has 14 (6 cab, 8 bed). The third row of mounts are the same style, but you would have to move them ~6-3/4" forward. The fourth and fifth rows of mounts are very different, you will have to cut off the front 4 pickup bed mounts (they are too tall), and swap the ones you need from your old frame.
Good luck.