I'd certainly look at unshrouding the valves. It's a lot of work (and should all be really close) but where and how much depends on the shape now, valve lift, stem angle, blah. Sometimes too open is a mistake, the flow leaving the seat wants to expand gradually and in the right direction, not turned loose all at once (like a vertical valve).
I wrote some stuff on the subject, some of it may be relevant: http://victorylibrary.com/mopar/chamber-tech.htm

Got a picture of a chamber?