Hey thanks for your help everyone, turns out that for some reason he decided to sell the car which he paid $3500 for $100 to a guy who is making it a paddock basher even though he was previously offered over a grand for it. He decided to tell me this afternoon even though he did it a week ago. So theres some time Ill never get back chasing parts. On the flip side this thread has given me some useful info about btr boxes.

Just to clarify a bit , up to AU internal wiring is grounded inside the transmission .   From BA on , the internal harness is different and the grounds to all solenoids go back to the ECU , so they are a no go.   There is also a variation in AU I came across . Although the internal harness looked the same the plastic plug into the case was a different size/diameter than the earlier models . Not really an issue . I only came across it as a mate built one , wanted to use the late case , then found his earlier case from a V8 EB or ED or whatever it was different where the harness fitted . Luckily I had an AU harness worked 

I'd imagine many earlier BTR's would be fairly worn out by now, either clutches, or even just the second/fourth band?   Not to mention potential gummed up solenoids, or valvebody?

interesting, 
A mate of mine's Dad's AU ute has an EL trans, and he's about to fit an AU trans in an XG (using XH transmission loom) 
wonder what's actually different. i'll reply here if he finds any issues with this combo. (assume the AU with EL trans used all the AU stuff though) 

Speedo sensor, gearshift indicator (sometimes referred to as neutral safety switch) and wiring loom, only external, internal wiring doesn't need to be changed

what electronics do you mean for this Thom?

   

All au trans will be a straight bolt in, just make sure you use the electronics from the car as one of the years has a different gear position indicator and I can't remember which one

Ok so b series transmissions are a no go? Ill see if I can get one from an au, any difference between year models?

Ea to au btr's are mostly interchangeable, in 6 cylinder cars with another 6 cylinder btr (some v8's had sports shift like ed sprint, el gt, au ts50 etc) to use an earlier btr in an au it is recommended to fit the au bellhousing to the e series transmission (straight swap make sure you get the converter re seated correctly), the e series bellhousing wilbolt to the au engine but it won't bolt to the sump, you'll need to use the au speed sensor, neutral safety switch and wiring, ba an later btr's can't be used in a ea-au (except maybe column shift ute transmissions but im not certain on that one) as they don't physically have shift positions for 1st to 3rd and are setup to run with the "sports shift" shifter, also unless it is a ute transmission it won't have a mount for the speed sensor (without it the transmission won't shift) as ba to fgx (except ba utes) all came standard with abs and use the abs sensors to tell the ecu how fast the car is going for controlling shift points

Yes cleaned and increased stall a little.     I thought that too, bought same one a decade ago for another car I owned and had not fitment issues. I wonder if the convertor was not seated properly on the flexplate and caused the whining noise?