https://www.primemr2.com/ has just delivered a gen1 to gen4 3SGTE loom swap to me and while we haven't finished putting it in, it does look the goods, which considering the number of obvious possible mistakes I could have made when I was considering doing it myself, is a considerable relief.
I got as far as obtaining the two new connectors from a wrecked Yaris and labelling them from an ECU diagram. It probably would have taken me years to work out which of the 10 or so of the wires of the 54 possible are actually used...
Turnaround was as advertised and support from Justin and his crew is outstanding