I did it, you will want to ditch the is300 ecu since it has an immobilizer and run a standalone (megasquirt is great on a budget) or find a aristo ecu with out the immobilizer and repin it.
The second thing you need to address is the fuel rail, either swap one from an older sc or get the drill and tap out so you can add a return line fitting.
Third: is300 DBW throttle body will not work so you need to get the older sc y pipe and throttle body, I am in the process of fabricating my own y pipe that goes to the intake plenum with a q45 throttle body flange.
Fourth: Is300 uses front sump oil pan, you will want a rear sump, I used one from a 1jzgte I also have one for sale.
There are other small things that I may be forgetting, I plan on making a more detailed build thread when I finish the swap. I've given my self until early May to get the project finished, this project has been going on for about 16 months so far, but there were times where I changed my mind and didn't know what engine I was going to use. Also not to mention I'm doing more then just a swap more like a full restore, new paint, suspension, bushings, subframe blasted, new hubs and wheel studs control arms, full interior needs to be taken care of etc... the list goes on!