I had a 1987 L555.
There is also another machine in the mix--my 555.
I could be wrong since it's been awhile since I had my slaes brochures but I think it breaks down this way:
553--gas engine possibly a Wisconsin, likley less lifting capacity than the 555's
555--4 cyl. Perkins diesel without aux hydraulics
555--3 cyl. Kubota diesel possibly with aux. hydraulics but not 100% sure
The 555's had different rear engine covers since the engines had different exhaust and cooling vents, and of course the decals were different.