30 hp can be found pretty easy on very weak built ( stock type) engines...Not out of the Question for sure....not saying the 4/7 swap cam will gain this kind of HP on any engine but not saying it won't either...the Higher the performance engine the less chance you gonna see these kind of HP number gains .
for that mater you can take 2 engines use the same Identical parts, same Builder using the same tolerances and One will make more HP then the other...there are many Theories and explanations but No-one really knows for sure.
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "