The 3385 had two pellets - an RA226 and an Americium 231. They were placed into an "L" tube and moved into and out of the counting chamber with an air pump. If you need a cutaway view please PM me and I will try to send it to you.
If you place a squeezeball onto the tube exiting the rear of the freezer and squeeze the ball, you should be able to hear the pellets and the 2 stainless steel balls (and spacer) sliding into and out of the counting chamber. You can always survey the tube and top of the counting chamber with a survey meter to see if you have any radioactivity.
The sample changer is hinged to the rear of the pig assembly, so if you lift up on the front of the table, it will snap clear of a small clip and pivot back out of the way. You can then reach down the front inside wall of the freezer and loosen the swaglok connector at the bottom of the elevator to remove the L tube.