Found the serial number. It was way up front on top of front crossmember. It was right next to the two rivets along the very edge of the frame rail. Thanks to all for help.
Not on crosmember. On frame rail where the rivets attach to crosmember.
Both of my 41 pus have the number as described above, in line with the front crossmember, near the rivets. if you think about it, it would have been a good solid place to hit, the frame would have more bounce further back.
When I replaced the front crossmember I had to be careful not to damage the area where the number was, it was that close to the rivets.
Mart.