https://resources.kohler.com/power/k...df/tp_2379.pdf
Page 12.10 lists 35ft-lbs for the bearing plate bolts on a K241, as Ken said.
As far as only 1/2” of thread engagement, that would more than likely be enough. General rule of thumb is 1 times the nominal screw diameter for steel holes, 2 for aluminum. Block is of course cast iron but I would think that ~1x nominal diameter engagement would be sufficient, especially since there isn’t a particularly large amount of thrust loading on that bearing/plate (or else they would have used tapered roller bearings instead of ball bearings
)
Btw, the fasteners in question are indeed 3/8-16.