I found what looks to be a bitsa or is it? Did they fit this top on some non self propelled Pros? It looks like a domestic mower with a sports body kit. I think it's non original as they're supposed to have a much larger capacity fuel tank.
Definitely been re-engined with what appears to be an early model V30. The lack of provision for a starter motor on the flywheel housing tells us the motor is pre 92. The mower deck is post 99 as to is the cowl.. I think they also ran with the larger snorkel, straight manifold and larger muffler on the pro.
I checked a parts catalogue (which reminds me I have to upload a few old ones I found) and the 505 had what could be described as a standard wide 'commando' type cowl - sans internal tank