Anyone know? Is the maxi ball joint the same size and taper to fit the cortina upright?

yes believe it is the same taper.

If it helps you. Its about 15mm long to the "bottoming" out or top of rubber boot and tapers in about 1mm at the the shoulder just before the top. Was measuring it with my new calipers the other day.

Maxi is the same as cortina. Its only when fitting maxi's to a sierra upright u get trouble.

Thanks