Mounting a Rear Sight

I just received a Plainfield Machine carbine but it has no rear sight.  I've found numerous correct adjustable sights available online. 

My question is do I need a sight installation tool or can the sight be drifted into the dovetail without it? 

Found a tool with great reviews and not expensive at all, but wondering about necessity.  Thanks in advance for any help provided!

Sure you can use a hammer to install and (re)move a sight. It's not a good method, but if you do try it, be sure to support the sides of the sight so you don't bend them and wreck the sight in the process.

Matrixprecisionparts.com makes an inexpensive and perfectly adequate tool for the job. It's probably the black one you are thinking of - a 5 star tool. I use one myself.

Once you've installed the sight, and before staking it more permanently in place, you can use the tool to easily move the sight any known distance, either to the right or to the left in the dovetail to zero your POI. In this way you retain full windage adjustment with your installation.

For example, say your carbine shoots left with the aperture centered in the newly installed sight. To zero, you can move the aperture and use up some of your windage adjustment or you can move the whole sight preserving full windage adjustment. Say you need to move the rear sight to the right by 0.05" to zero the POI with aperature centered. You can easily calculate this amount. With the tool, you can easily calculate how many degrees you need to tighten the screw to push the sight by exactly that amount.

Try doing that with a hammer instead of your head.