what is the center-to-center measurement of twin tall decks verses standard deck ?

Not sure exactly what you are asking??? Center to center in the same boat would be the same distance.

I venture to say 35-36"

My 12 meter is 33 1/2” C to C. Short deck with raised exhaust ports. With 2 1/8” stellings I have close to 1 1/8” clearance between headers. I wanted to go tall deck but was concerned about clearance. I can’t remember how to calculate the difference in width however thought it was 5/8” wider a side or a little over an inch less clearance. Don’t hold me to that though. If I’m drastically wrong I certainly cheated myself out of HP. 😂