Thank you all for the help/advice. They certainly look like XJ-6 to me, I'm glad that was mentioned because i had googled pics of XKE set ups and that didn't really seem to line up with what I had.
We just discovered the fronts have both seized open at some point along the way. Breaking was never very inspiring on this car. But I've effectively only had rear brakes for 'some' amount of time.
So for those reason I think I will try to find a more modern caliper, instead of going for direct replacements.
I know Wilwood is a popular choice on these cars for upgrading brakes. Does any one happen to know the model of those that would fit in place? It seems the XJ-6 mounting spacing is 3.5" so that is one limiting factor (it seems 'most' of their calipers are 5.25")