You have a choice between edlebrock, professional products, and trickflow there's more just those are the main. Edlebrock will change the effective rpm range of your motor it's designed for higher rpms and you'll also need special rails and other stuff to make it work. Professional products is a cheep easy replacement and comes in 3 pieces so it can easily be ported but you'll find mixed reviews on it (I had one and loved it). But the trickflow is the most exspensive but has a great design I believe the maximum single tb size is 75mm but I believe you can change it to twin. But for tb size I'm not sure. The thing with nitrous is it's a more efficient air so it's basically like a high altitude jet bringing its own air you wouldn't have to worry about a massive amount of it I would say 75mm should be good.