Berea's Round Top European is a nice double twist also... very smooth action...
Here is the trick for lining up the grain on the top and bottom...
Assemble the bottom of the pen without the mechanism holder...
Assemble the top of the pen completely...
Push the mechanism holder into the bottom of the pen just enough so that it is there, but not seated... you need to be able to take it out again...
Then put the refill into the pen and twist the bottom onto the cap... you will feel the mechanism turn in each direction to extend the refill.. twist the bottom so that the refill is fully retracted and look at the grain... if it is not matched, pull the bottom off the mechanism holder without twisting it.. kind of a wiggle movement.. then match the grains and push the bottom back onto the mechanism holder just enough to hold it in place and allow you to unscrew it... press the mecanism holder into place to complete the assembly... this will match the grain with the refill retracted...
Sounds a lot more complicated than it really is...