From what I remember reading about the 347" CHP the "E" version is optimized for favorable piston/pin placement to minimize piston rocking due to the low rod ratio, and a less compromised
oil-ring placement than you get in a typical 347" stoker.
Something about cylinder wear/ring wear being low enough to keep from getting more blowby, whatever, for at least 50,000 miles...whatever it takes to meet CARB certification.
They ran the tests and got the CARB certification to prove it.
I do not think there is anything inherently cleaner in the combustion chamber size/shape. Mainly, it is a C.A.R.B. LEGAL way to get a stroked 302/347 in a smoged Mustang 302.
The low emissions is due to retaining the stock cam, fuel-injection, cats, etc that came with a smog-legal engine, and MUST be reinstalled to be legal.
You just get a legal way to stroke the engine for more cubes.
Really, CALL CHP and ask what the intended purpose of that configuration is...they have lots of engine configurations, see what they recommend for a performance oriented, low annual miles replica.
Is Scotts Valley across from Shasta? Living in the shadow of Mt. SHASTA...if that baby ever blows ala' Mt. Saint Helens, it will really make Cobra emissions seem...silly.
Teasing...sort of.
You could avoid a "racing rich Holley double pumper" if you want to make a token effort.
Pete