G'day MF,
Hi maxwestern and paul_c,
that cowl could be seen from space (with a spy satellite anyway).
Why is it so big?
Styled in the mid-late 1970s - that must be one of the last motor models that Kirby made, before they exited small engine manufacture.
Have a look at the VC-Sports cowling, for Victa's version of that particular styling fetish...

Paul, that motor has an interesting feature combo; apart from the dipstick, the alloy muffler a la Kirby/Tecumseh 2-stroke is very unusual.
That would be one of Kirby's larger capacity 4-strokes; I'd say LKV 40 or VK40 models are likely candidates. I don't have any Rover repair manuals, as they're not really an interest of mine.
However, you may want to grab this one from the Bay of Fleas;
https://www.ebay.com.au/itm/Rotary-...nual-Series-99-1978-Edition/114195327915