Figuring out Dynamic compression

Short answer - nope.
The dynamic ratio doesn't change and can be figured based on measurements and cam timing events. Actual cylinder pressure will change with rpm so what you have at the starter motor cranking rpm is only valid for that rpm.

Edit - I'll add the MP 300hp 360 crate was a factory 5.9L Magnum with it's stock camshaft, equiped with an intake and carburetor.