Was the bushing loose in the shell when you put it together? With the OEM rubber bushing bonded to the shell to prevent this kind of problem, it stands to reason a loose fit on the urethane bush could have this going on.
On their website in the section on adjustable strut rods, Firm Feel makes note of the possibility of the lower control arm bushing sliding back and forth on the pin if you use a urethane strut rod bushing because the design is based on the thicker design for B & E bodies and not the thinner A body one, but they don't say anything about lower control arm bushings sliding in and out of their shell. If you push the bushing back into the lower control arm, does the lower control arm move out on the bushing again when you sweep the suspension up and down through it's travel? You didn't grease between the bushing and it's shell did you?
One things for certain, the problem is likely not to go away on it's own and you are right to start addressing it now before the car is completely back together, as not doing so will leave you with a car with control issues that will be unsettling to drive with at the least, and more probably outright outright dangerous. That's discounting the premature wear issues and possible parts breakage.
Looks like you have a Firm Feel greasable pin, have you called Dick Ross to get his input? I would think if anybody has an answer, it would be him.
