Glad the compression is good.
I am not sure you could have installed the (stock) balancer incorrectly unless you put it on backwards. There is a slot in the crank for the key, and the balancer has 1 has one slot as a key provision.
Spark plugs- I could see if they sold you to cold of a plug, and they fouled out that would cause a misfire shaking type response.
If your spark plug gap is not correct, and not all the plugs are firing correctly, that could also cause the issue.
So what did the end of plugs look like that you just removed? Black, white, brown?