Hello, and welcome back.
Lots of changes in the last 8 years, best way to catch up would be to go this website and read over
the rules and classes.
As far as amp ratings, don't quote me because I'm usually wrong, but I think as far as amp ratings
it would be the highest advertised(printed) rating. I don't know the case if it isn't rated in 4 ohms, but this is the place to find out.