273 commando heads vs. standard

I have read that the only difference between a 2 bbl & 4 bbl (HiPo) engine in 1965 is the pistons, camshaft, valve springs, and valve covers. The blocks and heads are identical. I have the 1965 Dart shop manual and it shows the 4 bbl engines with higher spring installed loads than the 2 bbl engines (as post 53 shows for 1967).