Poor old Tecumseh has had it, got it back together but suffering terminal sounding deep seated knocking noises although it started and revved up OK so was happy I'd got it back together correctly. Anyhoo decided I still wanted to save the deck and had another look on Ebay and went for one of these
https://www.ebay.com.au/itm/222503644174That's a hundred quid in real money!
Sooo cheap if it fails I'll put it down as a good learning experience
Had to muck about a bit to fit it as the Tecumseh was mounted to the deck with an adaptor, luckily it meant the deck was made to suit a B&S motor which this Chonda engine emulates. The crank length and diameter were different so I cut the O/Dia 25mm crank end off the old engine, bored it out to fit the new O/D 22mm one and make it slightly longer, cut a 5mm key way in it then made a custom key stepped to suit the new engines 5mm keyway down to 4.8mm to fit the old blade arm and 6.7mm tall to be a snug fit all round. The new Chinese crank had the correct 3/8 UNF thread up the guts so I could still re use the old mounting bolt for the blade.
Then I had to drill out the 8mm threaded mounting holes in the engine, tap these 3/8 UNC and fit the engine to the deck with the original mounting bolts.
Filled to 0.6L capacity with SAE 30, pulled the plug out and wanged it over a few times on the pull cord just to fling some oil around then added fuel. It started second pull and settled down to a nice even fast tickover on the auto choke. Very happy after I was initially startled by the awful rattling/tizzing noise which turned out to be the grass catcher sprung flap which makes a noise when the catcher isn't there...I'd never noticed before so I reckon the new motor must be pretty damn quiet! 6.5 Chinese horses just raring to go. I'll ditch the oil and refill after a few hours running and see what comes out!

Actually very impressed with the quality but remains to be seen how it goes over time. Initial impressions very good, quiet and grunty little work horse. Amazing value for money and sold through a reputable Aus wholesaler under their own brand name. My Googling threw up these guys as the most likely manufacturers. Quite a reasonable looking operation and another shining example of why there is no way that Trump's tariffs are going to bring back volume manufacturing to the USA. I really don't know how they do it for the money...
https://www.yantocn.com/four-stroke-gasoline-engine/rv200-2-gasoline-65hp-single-cylinder-lawn-mower-petrol-motor-vertical-shaft-machinery-lawn-mower-engine.html