I would be glad to offer an opinion on your problem, as I'm sure many others would. First, would you please describe what your exact symptoms are. I'm sure you know full well how it is behaving, but if you re-read your original post you will see that you didn't give much for anyone who hasn't ridden in the car to go on. Idle? Cold? Hot? Level ground or uphill?
As for the ground wire and mounting---the box needs to be secured as its position provides for cooling for the transistor circuit inside, the ground is external and I recall that it is run to a screw that secures a metal rail behind and slightly above the battery. Also try disconnecting the vac. line from dist. and see what affect this has. If the pickup coil inside dist. has a faulty connection or an intermittently open winding, it will often behave better when the vac. advance unit is not working the unit back and forth as throttle position is changed. Let us know the result and myself or someone that has seen one of your like models recently will likely give you more opinions or shared experiences that might be of some assistance. Remember this is the internet, not a job for most of us.