I have no experience of the cheap Chinese impeller that you are referring to, however, it will cost more than 500 bucks for an engine rebuild if the impeller disintegrates. Do the maths.
The correct way to fit the timing cover is to leave the dowels in place as they do serve a purpose.
The problem that you are having is that the front cover should be fitted before the mid-sump.
if you fit any other way then you run the risk of oil leaks from the front half moon packing immediately or in the near future.