I don’t know if this will help but I re-did our family roto-tiller a few years back. I think my dad purchased the tiller in like 1972 I thought it looked old then lol. It has a 1958 Briggs on it. I found all the parts on ebay to rebuild the entire engine using NOS parts. I even found a NOS gas tank for the engine, gas lines, etc. It took a while every week I would search for the part numbers I still needed and eventually they would pop-up in someones auction. Their is a person on their that even makes new decals for the briggs engines.
I will say your muffler on your engine looks to be original. Must be a low hour motor?
Hope this helps,
Joe