79 Lil Red Express?

I'm helping my friend Jim who bought a '79 in December, nice truck but the cargo box was replaced years ago. The wood on the sides and tailgate were never replaced. He bought the bought the kit and its ready for installation this weekend. The retaining bolts are 1/4". Does anybody know which size hole that the factory drilled into the sides and tailgate?
I'm thinking 5/16" or perhaps 3/8" to allow room for any easy fit. Any suggestions?
Thanks,
Tony

I’ll measure mine tomorrow, no wood on it but original. I’m thinking 3/8ths holes

We installed the wood Saturday and I drilled 5/16" holes and every piece fit easily.
Thanks

need pictures now.

contact me at rockpick43@yahoo.com, I have 4 images that I can send you.

thanks for the offer !
i just sent e-mail to you.

Holes on mine are 3/8.