Yeah, looking at your earlier pics I had a hunch you'd suss it out without too much trouble. You're doing a fine job of building yours!

With a kit I'd have to think those center points would have been indicated by small holes (not unlike those for wire stitches) where the mounting fastener holes should go. Even with that though, owing to the potential uncertainties of positions in any build, calculating them based on as-built dimensions may give a better result.

Do keep in mind that, once fitted, the amas should have a slight degree of 'toe-in' or at minimum have their long axis parallel to that of the central hull. 'Toe-out' is to be avoided at all costs!