that is advertised as "Telecaster neck pickup" should fit in that position, manufacturers have to make them that size - as you understand- to fit the rout in the body. They also have to make them with the pole peices less spaced apart because the strings narrow in slightly from the bridge to the headstock,this means the pickup width will be correspondingly smaller than the bridge or a Strat single coil.

It's very unlikely that any correctly sized Tele neck pickup won't fit and any advertised as such should fit or I think it breaches consumer law (but don't quote me) by being unfit for the purpose it was sold for or misdescribed(or something similar).

If you have tele copy the rout may be a little to small and may need some minor sanding or woodworking.

I have had no problem buggering about with single coils in a tele neck position and a couple of music shop guys and musos have said it's no problem to fit hot rails (type humbuckers), even to Squiers.

Good Luck..
That is all. :D