Our boats use an Isomat NG1 masthead which has an internal spin halyard using a small roller at the front which is not optimal but workable. The attached page from rigrite shows a blow-up of the masthead and also the optional spinaker crane which can be added to mount an external block. Requires removal of existing cover and drill and tap a couple screws.
NG1 Masthead
NG1 Masthead