I was wondering if a EB or ED 4L i6 would drop straight in to an EA (currently a 3.9L CFI)

yea with wiring loom, u may need the mounts off the 3.9, im not sure .. but if u have the 3 stage auto u will have to keep it, the 4 stage auto is longer and the mounts are in bit further back on the chassis, i had to cut mine out and re-weld them a few inches back. so its not worth it in the end for the 4stage.