In my humble opinion . . .
. . . I do not think it is necessary to bolt down the Bendix for the maiden run. HOWEVER, you do need to be ready to sit or lean on it when it starts to spin as it may want to jump to the right or left, depending on the direction of the drum rotation.
I have a 1945 Bendix bolt-down, and ran it with just water the first time -- out in the driveway. When it started to spin, it did a little umph to one side at start-up, and then spun just fine. When a Bendix goes into the spin cycle, it just goes full speed ahead -- 300 rpm. There's no speed build-up. You hear the thump of the solinoid, and it takes off immediately. It's not concerned about whether or not the load is balanced -- hence, one of the reasons for the bolt-down.
I have been advised by many members here who know a bunch more about this stuff than I do, that you should pour HOT (almost boiling) water into the tub and let it sit for a while. This is a good way to tell whether or not any of the seals are going to leak, and gives them a chance to expand against the hot water.
If for some reason you need to empty out the water without using the pump, it is simple to do by opening the filter behind the little door just under the main door. That filter is to keep foreign objects out of the pump -- bobbi pins, money, gravel. Just be sure to have a bucket handy to catch the water when you open the trap.
You've got yourself an extremely rare machine and looks to be in pristine condition. I wish for you the best of luck in getting it to perform. Mine works beautifully, considering it is as old as I am.
Good luck. And please keep us informed.
Jerry Gay