Custom Cages are not the MSA so why the need for a cert? Having quickly looked through the blue book, there is no need for handing over a certificate to scrutineering as Custom cages state on there website.
Aslong as it meets the requirements stated in the blue book for your race series/class then you are good to go
Geldy, that is a good point as the MSA does state the frontleg has to follow the windscreen pillar, but then it goes on to say "The mounting foot must not be rearward of the foremost point of the rollbar" so the cage to me is perfectly acceptable.
Murray