It's really frustrating to have the diagram and the part number, but no way to know what size the nut or bolt is.
Probably the best reference is the knowledge and experience of other Stovebolt.com forum members. Post a question about the specific bolt.
I haven't found a reference that defines the bolt numbers in the Assembly Manual. A few of the nuts, bolts, and washers can be referenced in the
"Standard Parts 8.900" group of the Master Parts Catelog with illustrations, but most of the hardware items in the MPC do not have the same number as in the Assembly Manual. The hardware item and dimentions are sometimes shown in the MPC section for the item that it attaches to, such as
this listing for Group #0.002.If you do find the nut or bolt in the MPC,
this list of abbreviations may help.
The drawing in the Assembly Manual will sometimes show you if the bolt is a hex, square, clutch head, etc.
You can sometimes find info on the item by doing a Google search of the part number and a brief description such as "bolt 3701135" for the outer bolts in the front engine mount of my '54 3100. Or, "washer 352282" for the middle washer on my '54 front engine mount.
Here is one of the "washer 352282" hits that gave me thickness info available nowhere else ...
http://www.wbparts.com/rfq/5310-00-447-2493.htmland info on "washer 365685", the end washer on the front motor mount at the same site ...
http://www.wbparts.com/nsndetail.cfm?NIIN=004496420&pn=365685Try the site to search for other part numbers.
I've found that some of the "bolt kits" or specific bolts sold by vendors are not correct, so don't assume that they know any more than you do.
Bottom line - I don't have a good answer.