Automatics are indeed quite capable on a drag strip. In most cases, they will consistently outdo (with proper gearing and valve body setup of course!) a manual transmission on the strip because they shift so much more consistently than a driver/clutch can shift. A very popular automatic for the drag strip surpisingly is GM’s PowerGlide 2-speed transmission, as it only has a single shift point. Not a good option for high torque/hp engines, but for street modified they do fantastic. Most muscle cars were sold with the solid intent of seeing at least some track duty (or stop-light drag racing), but the term muscle car in itself is misleading. This is why it is so specific to the car what kind of hp/tq, tires, transmission, chassis you will find on one. Factory muscle cars were fairly well defined, but drivers had a habit of taking non-muscle cars and turning them into one. This even led to some manufacturers creating non-standard muscle cars like the Cosworth Vega, the AMC Gremlin X, and the Mustang II Cobra in response to the post oil crisis markets. These were not honest-to-goodness muscle cars, but they fit the definition of being 2+2 coupes with large V8s (~5L) under the hood.
Here is a pretty good list of what was actually considered a muscle car. The general consensus is cars fitting this category began in the early 60s with the Wildcat and GTO. It is pretty safe to say by the 1974 model year, American Muscle Cars were completely dead. There were some holdouts, but they were nerfed to the point of only being hollow shells of the glorious street machines they once were. Even the coveted Corvette was completely nerfed (its inclusion on a muscle car list is academic only as it was technically a 2-seater sports car).
There have been quite a few recreations of these engines on the forums (including a few of my own), however I cannot recall any post-Steam release. If you have a specific engine, create a thread to request it. There are a few people on here who are quite adept at making these engines! I personally am heavily in favor of GM Small/Big block motors from the 50s/60s and have a few already made. My current 1955 BRC car is being powered by a 1955 Chevy 265 small block making about 200hp @ 4600rpm. It’s a pretty solid motor and is pretty close to stock production output values. I’ve already started building my 1965 BRC entry, which is powered by a 1965 Chevy 327 small block. I also have a 1970 Chevy 400 small block and a 1970 Chevy 427 big block in my barn.
EDIT: Here are the small block Chevy motors of the 60s using a 4 inch bore.
07CobaltGirl - Small Block Chevy 4.000.zip (86.8 KB)