zhandy,
I can't remember if there's an actual parts list on the 3A anywhere but I do have a 3B Parts Manual. IF the side mount radiator is the same style, then I'm guessing the mounting bolts could be the same too.
Here's what I have in my PM:
GROUP 14-01--RADI
ATOR
648438 Bolt, hex. washer hd. 5/16" - 10 x 5/8" (Acme)
648439 Clip, tinnerman, 5/16" - 10
4 ea to mount.
They don't look like normal bolts. I had to look up what an Acme screw looked like and sure enough, they have an unusual spiral to them. What you have now will obviously work. To me, if you want it to look like the original then the easiest route is to contact Harry Sheets,
http://www.midwestwillys.com/, - he'll probably have a whole bin of them whether the 3A is the same or different from the 3B. I had to order one from him as I could only find 3 when I was reassembling.
Be sure to get the matching clips too. Below is an image of mine.
Added: I needed to include the most important part. A 3A owner will be able verify if this is the type bolts they have or if it's different.