In structural steel work, the shear strength of the bolt is NOT the key issue
Joints work because of the friction between parts when the bolts are tight.
Same with boats. The clevis pin analogy is not relevant here. Clevis pins do indeed rely on shear strength, and good fit in the holes

You want the biggest bolts that fit. 14 mm is one idea.
However, I have too much experience pre-fabricating parts for our far away boat.
To avoid a nasty surprisse, be surprise you have 1/2" bolts available in case they are the only ones that line up.

Whatever you do, the bolts and plates should be bedded in something. If you use a resin/sawdust mix, that will guarantee a perfect fit, but you shoud grease the bolts all over to allow future removal.
I would bed in Sikaflex, or 5200, with grease on the bolts. The plate will not move