Specs for bed bolts ('79 SWB)?

[brossow]

Wondering if someone can tell me the specs (length and diameter) for the carriage bolts used to attach the bed on my '79 shortbed 2WD fleetside. I'm sure I could figure it out with measuring and trial and error, but it would be great if I didn't have to do that and could just buy what I need the first time. Bed wasn't attached when I bought it and although I don't plan to drive it immediately, it'd be nice to have the bed bolted down when I do.

Found a bolt kit on eBay, but no way am I paying $25 for eight carriage bolts that I can buy in bulk locally for $4/lb! (Especially when it appears two in that kit on eBay are far too short, based on the diagram at LMC:

and an old eBay auction:

Thanks a ton (or at least a half-ton),
Brent