If your current i6 is indeed an amc 232/258 I know the heep 4.0 motor is almost a direct bolt in. My old 74 had the 258 and I had swapped it out for a '90 4.0 motor. Bolted right up to the oem Scout 727 auto and was also able to use the original motor mounts off the 258 and mount them to the 4.0. Had to swap the 4.0 flex plate out in favor of the 258 flex plate. Also had to convert to electric fan due to the location of the 4.0 stock location of mechanical fan too close to the right frame