Both the 1G and 1JZ are available in front, mid or rear sump configuration, so it's just a matter of getting the correct version to suit your crossmember. And what makes you think parts for the 1JZ will be any easier to find?
Hmmmmmm I thought there was a USDM Toyota that came with the 1JZ... I thought I read somewhere that this was true.
Now I'm not up on my Toyota engine interchange, but what parts interchange between the 1JZ and 2JZ? are N/A and Turbo's the same? I'm mainly talking headgaskets, or water pump... I know I must change the water pump on the 1JZ (to a 2JZ) if I install that, am I correct?
If anyone has any links that would be helpful, please shoot them my way.