Despite collecting most of the necessary parts, I haven't built the 1.5JZ motor as yet as I ended up buying a complete track car with a Jap built 1.5JZ already in it - it's condition when it arrives later this month will dictate if/when I'll build a 1.5JZ locally.
There's a recent detailed thread on supraforums.com.au covering most of the differences but in a nutshell with the GE you will need replacement pistons/rings, drill/tap turbo oil return in the sump, source a GTE oil return coupling for the sump, drill/tap turbos oil feeds in the block, source a GTE oil pump, source a GTE CAS setup and harmonic balancer - this just to get the bottom end up to GTE specs - then add a headgasket, new head studs etc and your 1JZ top end. Quite involved when you start with a GE and want to do it properly.