Reviving an old thread. Like you, I had a built GX470 and a FJ60 - seemed to be the perfect match for me. I asked three top builders the same question. All three of them declined the job for various reasons but primarily because of the wiring. However, a cruiser buddy of mine was over yesterday and we were literally discussing this same topic. A local guy swapped a GX engine/tranny/xfer into a 40. Not sure of the rest of the details but I can get the guys contact info - he's a cruiser builder, fabricator, rest shop owner out of Lafayette, Louisiana.
You have a couple ways you could go with wiring. The easiest would be to pull all the wiring and computers from the donor vehicle and fit them into the project vehicle. Alternatively you could go completely standalone/aftermarket. And Tertiary you could splice new and old....this option is often the most challenging and problematic.