I forget- does the Yashica-Mat need a 3/8 to 1/4 bushing? If so, some of these bushings have a lip and do not sit down flush to the bottom surface.
If the door doesn't tighten up firmly, you can make adjustments to the latch. The small tab that sticks up and grubs the stud on the body can be bent backwards to get a tighter closing. Or you can add shim material around the stud itself.
People have used Yashica-mats on tripods for a long time. Yes, the back is not strong. Yes, you need to be careful, not stress the camera while attached to a tripod, etc. Yes, you need to accept that you will need to remove the tripod plate to change film.