That doesn't sound fun - I had exactly the same experience recently with my 1978 245 just after getting it out of storage, although I had some warning that the brakes weren't all that great and by the time they completely failed as yours did, I wasn't driving quickly and was ready with the handbrake.
I bought a new master cylinder, new spider distribution block and all flexible hoses from Brookhouse Volvo
https://classicvolvoparts.co.uk/
I bought 4 new girling calipers, discs and pads from Brakes International
https://brakeparts.co.uk/
I wasn't intending to change the copper lines, but I damaged some during disassembly - my local garage made up replacements for the three I damaged.
Write up here, with some pics and text about the brakes
https://www.volvoforums.org.uk/showthread.php?t=268976
To answer your question - any year rear brake calipers will fit. The two main styles are Girling (very common) and ATE (less common).
If you decide to replace the front calipers I suggest you buy the later style girling calipers for vented discs, which bolt on to an earlier car that had solid discs just the same (obviously you will need vented discs to go with them).
cheers