While we're very accessible by the T to Porter Square, the Masonic Hall also sent me this map to a parking location that's available for us. Just make sure to park in the rear of the lot, in a space not marked for the restaurant.
You need to print a Masonic Hall Function Attendee note and leave it in your car. I'll print a bunch and make sure they're available at the registration desk. If you want to print it yourself, it's in the comments.
The hall has some nice bathrooms that are suitable for changing in.