Someone here posted a good thread on how to DIY driveshaft customization.

if I remember correctly, you first mark the orientation of the yoke.

Then you mark the position of the weight.

Remove the weight, and cut off the yoke.

Cut shaft to length ( and swap in correct yoke if applicable )

Weld it up. ( short welds at opposing sides of shaft to minimize warpage / shrink )

re-attatch weight