Never, ever heard of them referred to as 'Spam Cans' in the fifties when I was among 'em. Always 'Flat Tops'. Then again, an Ivatt 2-6-2T was always a 'Teddy Bear', so what do I know? Perhaps I should take a nickname myself - the one applied to Marsh's LB&SCR I1X might be appropriate.
Happy New Year!
John