That was a racing category that has/had nothing to do with the appearance of the cars. There were various classes A/B/C etc Gas. That refers to standard pump gas and a vehicle weight category. Supercharged cars were in a different class or would be given a weight penalty, so a full sized blower car could race something like a NA V8 Morris Minor. I'm doing this off the top of my head, and it’s been a while, so someone will have to correct me or go into greater detail.
The gasser look with a straight axle is just a period look. On some cars, a straight axle up front was lighter than IFS, and the lean-back is to get more weight transferring onto the rear tires faster.
I used to be into drag racing. I really love the amateur stuff like period correct racing, the "gear jammers and door slammers", or even outlaw 10.50. If I had the time and money, I’d get back to the tracks.
Thanks...
I was into drag racing when I was a kid. Then the base I was stationed at in Germany had a air field & they shut it down one weekend a month and had drag races. I use to help out on a buddies team. But we were racing European cars & my buddies was a VW Golf with a warmed up engine. It was fun but different too.