How much boost do you want to run?
If your leaving the engine std and just bolting them on then you'll want small turbos for low boost but fast response, or will you need bigger turbos with a little more lag but higher power?
For the higher power option, 15psi, maybe T25's, for 10psi maybe T2s will suit or something from a Turbo diesel.
Youll also need manifolds fabricating unless someone outthere already does a pair of turbo manifolds for the Rover V8.
I guess Supercharging is better, but its much much harder to fit, get parts for and set up.
Maybe its a good idea to just get the V8 in and running first