I looked into this myself and found that for the money an M series swap is the way to go. You could easily spend twice as much on your R series and still only have the 140hp. I think the R series is a great motor and moves the Toyota 4x4s fine unless you are on the hwy or are running the bigger tires.

(aka suprathepeg, aka Sean)
89 v6 SWB truck "BLACK BEAUTY" EB valves, P&P head 30 over.
95 FZJ80. Lifted. locked and rollin on 33s (my dream machine)