Chongqing Zongshen is the OEM for Dong Fang's engines according to the EPA certification list for 2016 (the 2017 list has not been updated, and will probably be updated over the next several months if Dongfang decides to bring in 2017's) which was the last time Dong Fang sent a list of bikes to certify. You should be able to find a Zongshen branded engine easier than Dong Fang, and it might simply be imported as a replacement engine vs. a cannibalized bike used for warranty/parts (theorizing the source of your ebay engine, Bowtie). I would guess that a Lifan crate engine should work, but I would suggest to find a Zongshen crate engine first, if you can. But, again, according to the 2016 certification, Dong Fangs lists their sports bike, bobbers, and enduros (something like 6 or 7 bikes) under the same certification, so the sport bike engine shouldn't have been different than a bobber. Your guess is as good as mine (yours is much better since you have both bike and replacement engine )