8MM retainers/locks on 5/16 valves: OK or not OK?

What is the depth of the lock 'bead'? And the depth of the groove? I ask as from the dimensional info given, there is a radial different of .00125" between the locks. In the center of the locks they will probably lock in well... towards the ends, they will not be tight, but again, should only be .00125" out of fully inserted in the groove (or fully inserted on on end and .0025" out on the other end). That still leaves most of the width of the bead bearing the load.

308 lbs open is not all that high. It'll just be spending a lot of time there...

I suppose the concern is that the locks may shift back and forth, or just never be snug, and in case things float a bit, they might be more prone to pop out. But if you put 2 layers of standard duty aluminum foil between the keepers and valve (just over .0013" thick) to fill in the gap, it might just lock in snug and not move. Not necessarily saying to do that, but it's an idea of how small the gap is.....

BTW I saw in my .pdf Lunati catalog the 77118 and 77117 10* locks, which are listed for .310" valves (as opposed to the 77110 type which you started with and is listed as being for .308-5/16" valves). I do not know if these are square or bead lock types.