Can I fit an MTB freewheel onto my road bike?
Most freewheels use the ISO standard thread and are interchangeable. Some hubs have a 'British' or 'Italian' thread which are very slightly different but still interchangeable. See the Sheldon Brown page on freewheels.

I don't know where to look up the specs of older Shimano derailleurs. Googling for examples for sale on EBay etc. and looking for specs included in the product description suggests:


Min sprocket: 12t
Max sprocket: 28t
Total capacity: 28T 


So you should be good with a 14-28 freewheel.