Thanks all for your suggestions, comments and interest - it is appreciated. A "mid term update". I'll try to answer people's queries as I go.
Luckily we had friends in Melbourne where we could get the car towed to until we could work out what to do. 50 Km of towing From Ballan to west Melbourne via the RAA (RACV) cost us over $400 - hmmmm. There is more to that, but not to be posted publicly. We are Plus members, not Premium. I couldn't justify Premium, as even though it's only $5 a month more, that is times three (soon to be four) for a family membership, I've been a member for many many years, and I've had to call them three times in that period. Each time, they couldn't fix it (including a red motor fan belt), so I did.
We have decided to get the transmission rebuilt instead of dropping in a second hand trans. The box that was in the car (the one that is now dead) was a second hand unit, as about four years ago the radiator lower tank cracked internally and leaked engine coolant into the trans fluid cooler, which obviously then got into the trans and killed it. Back then, we found a low km 5L40E trans at a wreckers and had that fitted, as at the time a full trans rebuild was about three times the cost of buying and fitting a second hand unit. Thinking positively, that trans lasted four years and a fair few km.
Yep, a reconditioned trans is still not cheap (we tried a few places, and prices ranged from $4k to $6k). We picked a place that was fairly close to where the car was and had a lot of good feedback, and that is where it is now. Initial diagnosis is the usual 5L40E one - torque converter destroyed itself, and spat metal into the rest of the box to destroy everything else.
Is the car worth repairing - to us, yes. A mix of sentimental value, recent work (new brakes, new suspension, and we know its history), vs you don't really know what you are buying with another second hand car. This was our family car, and is now our daughter's, so it needs to be reliable. Oh, there is the fact that we are in Adelaide, and it is in Melbourne too. Makes things complicated. It is a Caprice as well, and they are still holding their value reasonably.
We used Fast Track Towing to get the car from where it was stored in Melbourne to the auto trans place (we didn't go through RAA/RACV for that second tow). They provided a very good service, and were happy to help out with anything else that we needed. a big thumbs up to them.
I'll post an update when the car is fixed. Repairs might take a week or so.