Transfering a section onto another window

I am working on a template, that doesn't show the result in what I am creating until I upload the file. That means, that I have to move these squares in order to make the lines line up correctly, and I was wondering if there was an easier way to do so.

I tried to make this model of what I am looking for.

The first two files are my template, where I create clothing for a game called Roblox. 

The last file is a recreation of what it is supposed to look like when it is uploaded and put onto the avatar that the templates will end up look like on. 

My question is if there is any extension or way to transfer the selected squares onto another window, where the final product will end up looking like. This will make everything so much easier since I have to line up squares and lines from the different sections on the template. Is there any way I can view it on another window, without having to copy and paste the different parts individually onto another window?