Yeah, their card looks like this (more slots on the other side):
View attachment 95978
You won't have any luck with the built in slots, they're not wired for it for a start. There was a sister card to the Performa that had an optional plug in RAM board. The design is mostly the same, the main difference being the Performa removes the expansion options for SCSI, RAM and ethernet or video or whatever the third thing was for.