1) Looks like <font color="blue">79f1504by4</font color> took care of that.
And, yes, the 4° change (advance) in cam timing will make a good bit of difference. [img]images/graemlins/burnout.gif[/img]
2) Open and Closed chambers refers to the design/shape of the combustion chambers.
Open are more of an O shape, while closed are more D shaped.
I don't recall the difference in CC's of each, but the open are considerably larger,
hence lower compression with every else on the engine staying the same.
Here's a shot of what a "closed" chamber would look like, albeit, my 351W, not 351M.
Note the "D" shape.
Ah ha! [img]images/graemlins/grin.gif[/img]
some good reading for you.