I got this Barnack style rangefinder for the lens that was included with it. The camera turned out to be in very good condition. All it needed was some cleaning of the view/rangefinder.
Tools: slotted screw drivers, flexi-clamps, tweezers, spannerwrench, q-tips, cleaning solutions.
The first thing to remove is the cover for the rangefinder window. If you do not have flexi-clamps then you can use pliers and a thick rubber band (to keep it from scratching the metal) … or even try removing it by hand if it is loose enough.
Pull out the window cover.
Unscrew the adapter ring.
Unscrew the collar for the shutter button.
The shutter speed dial is held on by three tension screws. Loosen them and pull off the dial.
The film rewind knob is unscrewed … you will have to hold onto the column to keep it from turning.
Completely unscrew and remove the collar lock. The rewind column will fall into the body.
The magnifier is held on by the ring screw, unscrew it with the spanner wrench or even your tweezers.
Pull off the magnifier lever.
Remove the two screws.
Remove the single screw just behind the hot shoe.
Unscrew the four screws to remove the hot shoe
Pull off the top plate.
This is a front view.
The rangefinder prism is on the left and the viewfinder mirror/prism is on the right.
Behind that is the rotating magnifier.
Clean the surfaces.
Watch out not to get any fluid behind the rangefinder prism.
If the secondary viewfinder image looks weak, it could be either dirt/liquid behind the rangefinder prism or the main viewfinder mirror has de-silvered. You can’t do much about de-silvering, but you can remove the rangefinder prism and clean the back. On the Canon IIF the rangefinder prism is held in place by two small screws and lacquer. Acetone or nail polish remover can soften the lacquer … do that or you may strip the screws. Once you clean it and put it back in you should check the image alignment through the viewfinder.
Attach a lens to the camera. Set it on infinity. Look though the viewfinder and then make slight adjustments to the rangefinder prism until it matches up or at least gets very close. Then you can tighten the prism.
Put the cover back on. Put the three screws and hot shoe back in to secure it. Attach the rangefinder adapter ring and cover window.
Turn the cover window to change the vertical alignment.
The vertical alignment screw is covered by a screw by the viewfinder window. Remove it, and then you can use a thin slotted screw driver to change the horizontal alignment. It the horizontal alignment is way off, it means the prism is not positioned correctly.
Once that looks ok, but the rest back on … make sure you put the shutter speed dial back in the right position by first pulling/turning the column until you find Bulb, then wind the shutter and attach the dial.
This Old Camera 
I am in the middle of replacing the shutter curtains on a IIF. Hoepfully you dont have to go that far with yours! sigh….
Ah, now that is an adventure. I try not to get that far in restoration, though I have done it, and it is something I don’t want to do again.
The shutter curtains on this Canon are in perfect condition, as is the rest of the camera … so it just needed a viewfinder cleaning.
That is lucky, mine were so hard, dry and cracked that they wouldn’t unroll without breaking. I am just now getting the camera back together after maybe 15 assembly / dis-assembly of the inner framework. I will not probably try this again.