91 xj only firing on 2 cyl

Hey guy's I've been around a long time and I've alway's found and fixed all other problems without help but this one's got me stumped. I bought a 91xj (4.0 auto) story was they (po) swapped in a motor (from a 94xj) and now have a no start condition. I changed the crank sensor and now it will start but won't run long and only has fire on #2 and #5 cyl. Any way they got the wrong flexplate on this motor? Any way the 91 would have a renix dissy and flexplate and they used the stuff off the 94? I did find a renix dissy in the hatch with some other spare parts....