You do not need an action block. All you need is a good vice. I use two half inch thick pieces of polyethylene taped over the jaws(Hardwood like oak will also do). I chuck it in the vice sideways so the picatinny rail and the bottom of the upper receiver are the surfaces in contact with the polyethylene. Don't over do it. For assembling AR's you should at minimum have an armorers wrench, torque wrenches in inch and foot lbs, and moly anti seize grease in addition to common tools.
If you don't have much gunsmithing experience then an action block might be the way to go. Mistakes are expensive.
