Personally I'll wait to see what Deejay says. It looks to me like an early (single deck) Scott Bonnar 45. If you post a few more pictures from different angles, Deejay will be able to confirm that and point out any non-original features it may have. If you include close-ups of the cutting reel, bedknife and chains/sprockets (have to take off the chaincase on the left side), he can comment on its general condition as well.
Because it is such an early example, it has a Kirby-Lauson engine rather than the Briggs and Stratton engines that came slightly later. This makes it difficult to set a date (the Briggs engines have year, month and day coded on them, but the Lausons are way more subtle). It would appear to be between 1968 and 1971, but Deejay may improve on that rather wide range.
