as long as you're certain that it is set to fire #1 with timing mark lined up at top dead center and not set to fire cyl # 6 which also lines up the same way.
If you align the timing tab on zero with the timing mark on the balancer align with the tab on #1 it will not leak out of the valves very much, if it is align on #6 it won't hold any pressure at all due to it having both valves opened on #1 overlap stroke with #6 on the firing stroke
Either way if it isn't on #1 TDC on the firing stroke you can move the hose to the other cylinder at TDC on the firing stroke (#6) and start testing from there
