I have a 3422 that does 50 X 4 and is 140 X 2 at 4 ohms bridged, so I am assuming that amp is a little more than that. (Amp not for sale, just offering comparison to help out)
I honestly don't know if it is underrated but it pushed my Germaniums pretty good, I was impressed by the lil thing lol.....dimensions are...10.9x2.7x9
If you still want it, PM me with how you can pay, and you can look in my sig for refs.