Hello ,from my experience unless you want more than 475 bhp what you have will work ok with 4 injectors maybe some of the 800cc siemens would be best . So far we have tested the std 4b intake and made 480bhp max rs500 type is ok to 800bhp and magnesium rallycross type max 860 bhp and the swedish style plenum cover over std primary max 740 bhp.As for the plenum spacers they never make any difference on any manifold we have tested on our dyno....not even 1 bhp . A common conversion for the std 4wd manifold is to use the throttle pot from the late escorts as these are bigger and help to get to the magical 500bhp...Hope this helps...........