A 427 Windsor is just a stroked 351, so it will fit right in. In 67 Ford widened the Mustang to accommodate the 390, which is much larger than the 351. You could even drop in a 427 or 428 FE motor if you want.
The link shows a 67 Mustang with a 351 Windsor in it. You have tons of space.
OK..First of all the real 427 is a big-block based on the Ford FE engine series. Ultra rare, ultra powerful. When you say windor-based I assume you are referring to a 351 Windsor based stroker motor. The answer to your question is yes either way. The real 427 big block will fit as it was offered in 1967 as a Shelby powerplant, later replaced by the 428. The Windsor based small block stroker motor will fit easily as well since the 351 Windsor and the 302 are dimensionally very close to one another...I believe the only difference is the deck height of the block.
It'll fit, but will be super tight. and unless you spring for the all-aluminum 427 (which IS NOT cheap), your car's handling will suck. I would suggest rebuilding your 302 with a 351 firing order, some flat-top pistons, nice heads, and a good intake/carb. It may not make quite as much power as a 427, but it will save you weight and will honestly be more fun to drive.
First of all, there is no such thing as a 427 Windsor. The Ford 427's were called FE blocks. And yes it will fit. You will have to cut the fender wells a bit. Then when you go to change spark plugs you will have to pull the motor mounts loose and jack the engine up. But it will work.