[LMH]

A little bit of a guess on my part but I'd say that comp cars back then used for endurance racing would have the bigger bulkhead. Every little bit of gas you can squeeze into the car would be important. Looking at the cars now, they could be either way as restorations may have changed what once was original. I saw that no-brace thing as well on a number of pics but I have no idea why it's like that. I sure wouldn't want just a hoop in it.
Larry