Whether details on your restoration or just simply wanting the right hardware, this is your last stop, (next to your manuals), well kinda.
The "special" hardware has part numbers in the manual but those part numbers mostly will not help you in any way to find the size, pitch length or type of head. Months of detail work checking my original vehicles and others I have dialed down on the correct hardware for the span of the M151 series run.
Many of the "special" fasteners where SEMS. This means they had integral washers (the washer was permanently part of the bolt or screw), this could be an external or an internal star type lock washer. The head types varied fairly from Slotted pan heads to indented hex heads and lots in between. Many of the kits below that were originally SEMS hardware are now a separate correct bolt and correct washer, as some of this type of hardware simply does not exist, or exist in any quantity to provide it for sale.