This is what you need, Martin, 50 amp, $216 plus shipping(and plus VAT for you poor souls in the UK!):
https://www.autohausaz.com/pn/91160312000
It has an internal regulator, so that makes wiring a snap. I punched in 1971 911T with a 2.2 litre.
A new alternator HAS to be cheaper and certainly easier than fabbing a vane thingy to fit.