Thanks for all the advice, ended up going for a new Chinese heater from a reasonably well established ebay store. Could only justify spend on one (rather than getting two for direct replacement), but I think the installation can be done to make it simple to swap with a similar model when it fails.
Ran a thorough bench test when I received it - lots of smoking on first start but all seems fine and have tested restart from both warm and cold. Only slight snag was after a slight adjustment on the bench and turning round twenty mins later to discover it smoking! A panicked switch off ensued and discovery that the adjustment had pushed the fuel line against the exhaust and it had melted and was oozing diesel. Yikes. New better quality fuel line on order now, plus a more sensibly sized and oriented fuel tank. Generally quite impressed, although I'm under no illusion that it'll last for any great period.
