With 9:1, 290 duration is about the limit. Pull your valve covers and see how much valve lift you can get away with. Check for valve seals clearance and coli bind. I ran a 286 with 256 @50 and it ran very well. (180 in a roadster.) Any cam grinder can improve on you @50 numbers. Check thinks out and I think you will find your option will be limited, without doing additional engine work.
Hopes this helps
