"...It would really help history if we knew the real story on the Swiss Cheese cars running in NHRA (maybe in B/FX?), how they ran, what class this car ran its 12.27 in, etc."
I just read that post. Probably can't answer all the questions. But, I'll share some pics & info I have that might shed some light on it.
Have pics of the Royal Pontiac car that Jim Wangers drove. In one of the pics, he is running against a Stan Long Pontiac B/FX Pontiac, probably running for the B/FX class win, which Jim won, at the '63 Nationals. I'll post the list which shows his ET, which was 12.59. Also have a pic of what appears to be that same car, with A/FX on it.
Also have pics of the Anderson Pontiac car, with Arlen Vanke driving. I don't know how many cars these big dealers had, that looked exactly the same. So, I can't say if they had different cars for different classes, or just made changes to meet different class requirements. Also don't know how the different tracks classified the cars. I'm guessing that some track tech guys probably put the swiss cheese cars in a Stock or SS class, if they weren't running the FX classes there, so all the cars could race. There were probably lots of mis-classed cars before that time & since.
The last pic shows Arnie's car, with A/FX on it. He ran lots of different classes, with several cars.
Note: Bottom line is that you can't believe everything you read online or in print. Also, this stuff happened almost 60 years ago. So, who can say EXACTLY what's true & what's NOT true about all the details from back then.
Here's some stuff about the 421SD engine that some may enjoy.
https://www.nhra.com/news/2021/421-n...orever-footage