hmm.what one of my friends did down here was put a nissan SR20 in his samurai.fuel injected,the works.it runs like a biach,did 15s or higher on the 1/4 mile.but has stability issues.best swap is a 16V vitara engine,best power/weight ratio.
also there is a guy here who put in a rotary engine from an RX-7 in his sami,not too sure which one it was,but.....that's an extreme case,not really an offroading vehicle anymore,more a street sleeper.