Fitting a CB Performance oil breather kit to a type 4 engine on 1976 Double Cab

50mm = 2"
Fat pipe all the way if you can, that's why it has a 15mm outlet. Try and avoid water pipe, it doesn't like oil and will likely kink and block up when it goes soft (in next to no time).
Someone will be along shortly with a link to fittings for your filter top.

 

The type 4 carb type breather box works fine vented to the air filter, just give it a clean now and again. Don't need anything fancy like the you can get for the type 1 uprights.