I think the Qualcast reel mower that looked like a tiny Villiers parked on top of a manual push-mower was reasonably common, but the Super 14 does not seem to have been - it probably cost a fair bit, and had to compete not only with ATCO, but in Australia with Scott Bonnar and Victa as well. Nevertheless I don't think the mower is rare, or especially old, from the design and the number of threads about them on Outdoorking.
So far as dating the Suffolk engine is concerned, you might try one of the British sites, such as this one:
www.stationary-engine.net/forum/or this one:
www.oldlawnmowerclub.co.uk/If nobody there can help you, it is going to be quite a challenge - but I'd be surprised if they don't have at least the best information available.
