G'Day xemeanmachine. You have one GIANT pm waiting for you
I'd say go the Tremec TKO and forget about the rest
but they're way too much $$$ for your application. The next options are Supra or T5. Just a note, TTC (Transmission Technologies Corporation) has taken over a few companies so now a lot of gearboxes get called Tremec now, eg: Tremec T5, which is not the original bullet proof Tremec TKO. Just background info.
Mal Wood in QLD is the best for getting info on kits for a Supra or T5 conversion. He's bailed me out of jail a few times
Keep scouring your local trading post for guys wrecking whole cars or selling gearbox/conversion parts. Get all the bits cheaply and then perhaps order the other big parts from Mal?? Not sure what he charges for the Supras or T5's. Call him and see which one of those 2 suit best.
ps: Still loved my Toploader though. Unless your running 4.11's (like me) and highway driving sends you nuts @ 3500rpm, then consider a toploader, because they'll drink a Supra or T5 under the table. They love you to beat them hard!