955K's and 955L's look the same, the earlier model H's have a slanted hood.
Well, a lot of tractors all look the same if you don't look close enough. There's a lot of changes between some models, and they're usually identified by obvious engineering/design changes - but the 955's are a curious model, in that Cat went from 955K to 955L without a serial number prefix change, and the engineering/design changes between the two were subtle.