Fan,
A 369A is an OH6.
A 369HE is an "Executive" version of the 369HS, the only difference being the interior trim panels, and the 369HM is a military version with a different wiring harness etc. All these aircraft have a civilian FAA type certificate.
C20B engines can be installed in place of a C20 as long as C20 limitations are observed. Try finding C20 parts these days!
CGWRA
The spar of the blades is steel but the skin is fibreglass very similar to a 300. I doubt you can find them any more.
Fibreglass blades