[Modena]

Usually one end of the driveshaft assembly is plunge and the other is not. On VE Holden shafts the plunge end is held on with with a large circlip around the outer of the CV housing, removing this circlip allows you to pull the CV housing off then there is another small circlip on the shaft that holds the splined portion onto the shaft.

for the other end there is a snap-ring on the shaft within the housing so that housing can just be tapped off with appropriate soft hammer.

Your idea of machining a slot for an inner circlip sounds like it might work?

round-tube Classic Revivals use custom made shafts which are the same ends as factory VE, the shafts are just 65mm shorter, and they cost about $450 each (ouch).