The one time that I replaced a Beta head I fitted the exhaust manifold first. Isn’t that the easy way?
Probably so with the standard exhaust manifold, but mine is an Ansa/CSC that has been cut and shut. This is what it looks like. The manifold to head aren't the problem; it's bolting up the two flanges where the pipes have been cut (ironically to make fitting easier) with very little space around it and lying with your nose brushing the sump...