I'm torn on this one. I see the same. I may have had bolts on mine decades ago but am going to try the wing bolts to see how they do.
When you go to the 3B Page Engine link on the Tech section, you can see a bunch of engines. In addition to Lawrence's '55, here are some more examples:
Hi guys, As I progress on my restoration many questions arise. This is not stopping me but I would love to go for what is actually correct. When I see Wade's photo references I can see that the air cleaner bracket is with bolts to the firewall. Reading my 1956 Parts List manual it lists wing nuts like 2A and MBs.