Believe different corners angled = big block - small block applications
There are also reinforced and unreinforced versions as well as the early and 6 cylinder versions as Charles mentioned
Guess this subject is going to take a while.
Let me dig through the pictures and start posting what I find while others post their findings.
Sure everyone understands how often these brackets can get swapped from one car to another especially when they are rebuilt or the engine gets swapped