If you have little experience with wheels, you are in trouble. But it is the kind of trouble that study and practice will fix.

The following suggestions assume that your present wheel is true and properly dished already.

Basically, and I am ball parking here, you will have to move your hub about 2.5mm towards the drive side. Replacing/removing spaces will accomplish this. Of course, once respaced, you will have to center your axle in the hub and set bearing clearance.

With the hub moved to the drive side, the rim will be out of center with the center line of the frame set and must be moved 2.5mm towards the non-drive side. To move the rim, loosen each spoke on the drive side by one exact full turn each. Hold each spoke with your fingers and loosen the nipple. Ensure that the spoke is not winding up or down.

Winding up, or down, is what happens when the nipple catches the spoke threads, forcing the spoke to twist with the torque applied to the nipple. You must not allow this wind up or down to remain.

After loosening the drive side spokes one full turn, tighten the non-drive side spokes one full turn. Now check your dish. It should be pretty darn close and you should have more acceptable chain line. Repeat as req'd to hit dead center.

Hope this is a help and, for more information pertaining to how to convert old bikes to single speed design, you are welcome to visit my custom bicycles page, and seek out the sort of information that will help you with your project.