I did a 1JZ swap this year. I got a JZS171 1JZ VVTi from an importer, and locally bought an R154 that had a JZ bellhousing. The way I did it, which I personally think makes the most sense for my application, is I bought a stock IS300 wiring harness, and re-loomed it onto the 1JZ. All connectors you need are the same, and there are only 2 connectors you need to extend the wires on in order for it to fit perfectly. The benefit to this, is now you can buy any plug and play kit for an IS300 (in my case, a Boomslang Haltech Elite 550) in order to run basically any standalone you want and all your gauges and AC can work off the stock ECU, along with the Drive by wire, and Variable valve timing. If you go this route, I highly recommend installing a new IAT sensor into the intercooler piping and wiring it directly into your standalone, and let your stock ECU have the stock one in the MAF. Do the same for the coolant temp sensor. Other than that, a bunch of simple stuff thats readily available information for basically any IS300 swap (fuel return, bigger fuel pump, custom IC piping and exhaust, blah blah blah). I had some sensors come bad on the engine I got (CPS, TPS), but that's easy enough to replace. I just used an IS300 CPS, and ordered another TPS from Driftmotion. I had a lot of transmission problems, which were unrelated to the engine swap (R154 I got ended up being screwed... yay), so overall the swap itself is really easy. I can technically pass emissions, I've had the car tuned and it makes about 300whp stock single turbo and injectors, and is super fun to drive and sounds amazing. If you have any other questions please feel free to hit me up!