G'day wce,
Those blades you have fitted are in fact Turner P/No 50-07-18, an early 1960s type which continued to be used on side discharge Turners until Turner exited the mower industry in 1970. These are long unavailable.
The P/No 50-15-18 'fan' type blades shown in paul_c's post above were introduced for rear catcher Turner models around 1964. These were fitted as a pair, rather than a set of four.
There's a bit of discussion on these blade types in this thread about a Turner-made 'storebrand' model;
https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/72964/3.html 
