yes, its been done. there was a ute for sale last week on here.
it was a FJ20ET.
i would ask why an FJ? a SR has a lot more potential and a wider aftermarket following than the old FJ. also lighter and smaller.
for that litle bit extra price up front, u can have an engine that will cost u less in the long run.

the sump should be ok.
the tranny tunnel will need a new hole for the shifter (shifter more towards handbrake on FJ 'box)
have a look at Maddat they make kits for the FJ into 510. perhaps a rough sketch for ur 1200 can be drawn from what they offer.

cheers and let us know how u get on