Uh huh.
Mikuni-Solex's are actually the factory carburettor for 18R-G and 18R-GU. That would be a factory manifold also. I wouldn't really call them a 'performance' bolt on, although the bolt on part is accurate. The bolt pattern on the manifold is the same as Weber DCOE side-draughts.
These are good reliable carburettors, I would recommend whoever buys these checks the main jet blocks are screwed down tight and correctly seated as this is one of the most common issues for these.