How will a engine act if not balanced correctly?

[Street Fighter]

I am wondering if I have a engine balance problem.I say this because I ordered a set of pistons and a crankshaft kit and placed it in my camaro's engine,but I can't remember if it was ordered balanced or not.Anyway the flywheel is stock and so is the balancer.I have a bad vibration at 80 mph.Wouldn't there be a vibration at any speed if there was not correct balancing of the engine? Plus it seemed to be in the rear of the car.give some ideals.This was done about 5 years ago so I can't remember what I ordered, have had this promblem for years. Don't drive the car enough to be able to pinpoint when it started.

[Mean Green Z28]

Engine balance you'd def feel when the engine is running and you'd think it was a bad cylinder/plug cos it acts hella stupid. What you described is more of a driveline issue IMO