The Componon is a variant of the Symmar that has been optimised for high magnification work, i.e. enlarging and macro. It had the same elements in the same cells but the spacing was slightly different.
Early Symmars were in Compound 3 shutters, later they went to Copal 3 which is a larger thread size so I imagine the Componon would be the same. As Jackpie has said, most donor shutters come with the lens attached and a 300 Symmar probably falls into that category so you would be better just waiting for a bargain on a 300 Symmar than fiddling wit e Componon.