Less severe problem than unbalance driveshaft due to lower rpms. Seems to me OEM half-shafts had no factory balancing. At least none that I've seen have any weld-on weights.
A driveline specialty shop can balance 'em for you if you got trouble.
How did you check balance? If you MUST (not recommended) run engine w/ car on stands, be sure to put stands under wheel hubs to keep half-shafts close to normal geometry.
On the road, half-shaft unbalance will feel same as wheel unbalance due to same rpm. Probably not noticeable till you get to super-legal speeds.
Next time be sure to mark alignment of all parts prior to disassembly. I learned that the hard way, too.
Ye ol school o hard knockers!
Good luck!
Al
PS: OEM u-joints highly recommended. These include precision clips for accurate centering/preload of u-joint. Several horror stories related to aftermarket u-joints in the forum below.
