Cooler intake manifold

I would also consider the climate where you live before completely blocking off the exh xover. You do need some heat in the intake to vapourise the fuel for a street driven car. It is reqd for good mileage AND good distribution.
I live in a very mild climate. So I often block off exh xovers with a steel plate. For somebody who might live in a country area where they have 0* C in winter, I drill a 1/2" hole in the block off plate to allow some intake heating.