There just aren't many wideouts with the physical frame that Montgomery has who have great success in the NFL, but the one who has is an exciting comparison.
Ty Montgomery is almost historically unique. He checked into the combine at six feet even, and 221 pounds, but Pro Football Reference lists him at a svelte 216. The only other NFL receivers since 1966 to be six feet tall or less but at least as heavy as Montgomery are the following: Josh Morgan, Tamarick Vanover, and Marcus Vick.
Only Vanover was drafted as highly as Montgomery, and superficially he's not a bad comp.