Here is the link to the mass. See it before the SSPX takes it down. By the looks of it they could easily fit the attendees into the Sanford chapel.
I don't know about the size of the Sanford chapel, but this is a constant issue for confirmations, and most chapels just deal with it, reserving spots for the Confirmands, their Sponsors, and their family first ... and the rest are mostly there to experience a Pontifical Mass and are there first-come-first-serve. This was nothing more than an excuse used to acclimate the faithful to closer cooperation with the Conciliar Church.