No need to go on the internet.Roy Nacewiz has the nuts listed in his catalog.$5.95 a pkg.Looks like 11/16 - 18. Not going to find that at the local hardware store. Guess it's time to jump on the Internet. Thanks.
................The 40 and 41 OEM truck sealbeams used the same size bucket as the 35 passenger car and the mounting bolt appears to be the same as well making them nice to use on a 35 passenger car or a 38/9 pickup if you want sealbeams without having to use one of the kits.
Those look like you could find a plow bolt pretty close and drill it out on a lathe.If you have one original sample, have someone who owns a lathe make some for you out of bar stock. Another thought would be to find standard carriage bolts that are close enough to the actual part and final machine those to make what's needed. I have looked at these original bolts in my '35 passenger car and pickup truck headlight buckets, and with my amateur machining skills, I think I could make these w/o that much difficulty on my little maintenance shop 5" swing, 48" bed, South Bend Lathe.