Dave have you spoken to Barry Ward at Hi-Tough Engineering Pty Ltd U3/ 7 Ryecroft St Carrara QLD 4211, (07) 5530 4123?
This is the successor company to Maxi-Drive Axles. I had them make up specials to hybridise a Series IIB F/C to stage I swivels. I needed to send them the ENV diff side gears and all the dimensions and now they are a standard part available on order.
You should be able to send one of your end caps and the broken end of the halfshaft and they should be able to machine them up. They will have the brooch to cut the diff end spline so it's only the hub end they need to replicate.
Diana

