I built one of those some years ago when I refurbished a rusted up 99. The Chinese HC is less smooth than a genuine Singer but works fine.
I have the same problem with the case interference fit. That is because the older cases built for HC machines is actually a bit longer on the right end.
You can remove some material from the inside of the case, about a 1/4" should do, bore a hole all the way through then patch it (not my choice), find a modern larger case, or keep looking for a HC compatible case ( what I'm doing)
Joe