Is it worth replacing the driveshafts if the cv boots are torn but they sound like they are working fine?
Should I just wait until they start clunking and replace them then, or should I get onto it?
How hard are they to remove? Are those 6 allen bolts holding them in difficult to remove after 30 odd years?

If the CV boots are torn = Replace CV boots
If they start clunking = Replace CV joint

You've got the 6 bolts on the gearbox end & 1 massive 32mm nut in the hub