Half shaft breakage is not a problem - a very slight inconvenience, more so if you FWHs.
You just press the yellow lever down and continue on your way
Easy enough to carry a long & short drive shaft if you are going on long journeys away from home.
Look upon the drive shaft as a fuse. It's the cheapest and easiest component in the transmission system to replace.
I don't think 24 spline shafts are any less prone to snapping
The problem is - after 60 years OE shafts might be prone to failure.
How you use the vehicle matters - gungho off roading in mud pits with massive wide tyres puts a bigger strain on the transmission.
If you break a half shaft - replace both sides as a matter of course.
If the vehicle is new to you, then you will have no idea of the provenance of the shafts.
Make a note in your maintenance log book when you replaced them. Driven sensibly your new shafts should last many miles and years.