Mal Wood (in Brisbane?) seems to be the duck's proverbial for manual conversions. You're not limited to the factory V8 box. You could fit a Tremec 5 or 6 speed, a T56 or possibly one of the stronger Supra boxes. You might find it hard to source an
ECU for a manual though (you have to either change the computer or wire yours up to think its always in neutral AFAIK).
If you go this way though you'll think $3000 is cheap by the time you finish...