Muncie M20 Ink stamp

[P.J.]

I recently pulled out of the garage an M20 muncie trans to clean the years of grease and grime that the trany accumulated. The trany has never been opened and sat in a garage for 20 years before I purchased it. I cleaned it with oven cleaner lemon sented as recomended on a previous threat.The cleaner works great. The steel tag reads 3952659 WB
the assemlby date is POD28A the vin number is 20N117375 661 case after I cleaned the trany an ink stamp WB was cleary visible on the top of the case passenger side about 1 inch
high letters. I have never seen this before. was this stamp
used only in this plant? or were other asembly plants using
an ink stamp.
suprss70