is called a what? Ok, tell me how to measure to get the right degree. Should I shim the tail of tranny or the rear end?
Any suggestions on a brand and how much should I expect to pay for one.

i believe the tool is called an inclinometer. to measure trans angle i think you run it along the pan rail or the pan so it is parallel with the output shaft and same with the pinion. as far as what to adjust i'm really not sure. good luck.

they make an 'angle finder' at sears...

Got mine at Sears.

Protractor, aka "angle finder".
About any hardware store or home improvement center should have one, ask for a protractor and they will (or darn sure should) know what you are looking for.
As for shimming, check the angles first, but usually you will shim the axles with wedge shaped shims.