I need some clarification
 

My wheels have the standard 120mm track spacing. My conversion is 126mm, so spacers would be needed. Could I just go to the hardware store and pick up some washers?

One more thing, my front hub is 100mm, while my fork is 96mm. Would cold setting work?

I've searched.

You can probably just use washers but it may affect your chain line. I'll let people with more experience chime in.

As for the fork, that's 2mm off on each side. I wouldn't even bother cold setting it, though theoretically you could.

What should I do for the fork? Just wedge the front wheel in?

Ya, 2mm on each side isn't that much

Alright. Thanks.

As for the rear wheel, does the washer situation sound like a good idea? 3mm on each side?

(I'm assuming you have a steel frame.)

Cold set the fork, all it takes is a pair of candlesticks and some arm muscle. For the rear, you can skip the spacers and just squeeze your dropouts when you tighten the track nuts.

Yeah, it's an old steel Centurion. I just discovered I have another dilemma. The axle on my new wheels is bigger than the opening for the axle on the fork.

File the fork tips. I had the same issue.

That's what I was thinking. Thanks for everyone's help!