I always felt Shilton was a little over rated. HE was good, but he was talked about as the best in the world and he was clearly nowhere near that. Apparently he had abnormally long arms which helped alleviate his lack of real height, gave him a bit more reach.
If you look at the greatest keepers in our memory: Buffon 6'4", Schmeichel 6'3", Seaman 6'3", Taffarel 6'0", Schumacher 6'1", Zubizarreta 6'2", Chilavert 6'2", Cech 6'5", Southall 6'1", Kahn 6'2", Zenga 6'2". The best 70s-80s keepers were 6'0" to 6'2". The 80-90s were 6'1" to 6'3", and now it's 6'2" to 6'5". It's following heavyweight boxing where dietary changes mean that players are getting taller as a minimum requirement to be able to compete.
Back to the original point, 5 foot 11 as a keeper was small even in the 80s, but it's career limiting in the modern game.