Don't know that car, but here's a couple of ideas...
Is there any wear/damage to the driveshaft and cup?
Did the instructions call for o-rings to be fitted in the cups, if so are they there?
Even though the rods were fitted as the instructions said, do the wheel angles look right?
Were the shocks assembled to the correct length? Too much travel could make the dogbone fall out.
One good hop-up on all cars are universal joint/CVD driveshafts for the front of the car, these are very unlikely to fall out, and smooth out the transmission at full lock.