I've had it confirmed by a porsche guy, that the only difference between the 86 turbo and 87 on turbo driveshafts is the number of splines.
The earlier ones being 33 splines and later ones 25 splines, so as long as you are buying them complete with CV's it doesn't really matter.
The lenghts are exactly the same for both versions.
I've now got a set of 86 turbo driveshafts on order, so I should be sorted, but I hope this info is helpful for anyone else doing this conversion.
