I think give them another chance to fix at their expense.
If no joy, any ideas how muffin is placed for a full/partial refund ?
dear oh dear.
maybe ask them to pay for it to be sent away to a proper engine builder place, worst case, id even compromise and pay half the price just to get it sorted!
someone like this
http://www.scholarengines.co.uk/
Smokes back
Heard these stories a million times where people have had ongoing/recurring problems with rebuilt engines. Usually it's by specialist Japanese tuning shops.
My opinion is that these places are usually run by hobby mechanics who are out of their depth when it comes to engines or anything genuinely technical.
Hondas are notoriously hard to rebuild unfortunately.
Then these "specialists" shouldn't be offering services they cannot reliably provide.