this isn't even a high rpm cam for a 302. the duration numbers you mention are pretty insignificant. what is the spec at @.05"?
i seriously doubt you are making that kind of hp with a 347 and those headers. 1 3/4" would be more like it.
and 12.5:1 on an all iron motor? what kind of fuel are you running?
with all of that cylinder pressure that small cam and those headers are
huge bottlenecks.