There isn't much if any difference between them. Not all the 500 series had mechanical governors, there was quite a few with the air vane governor. Conversely they also made some 450 series with mechanical governors, the one's found on a 16inch "909" or "Automatic"( I can't remember which one now) which was also fitted with an engine brake on them.
Last edited by bigted; 13/02/22 01:25 AM.
