put in 8 3/4, now have vibration

If it were me I would call around to some other shops in the area, the 200 they charged you is out of line IMO. Like I said I got mine done for 90 bucks.

When you find said shop ask them specifically how they want you to measure it. The shop I use wants a measurement from the end of the tailshaft, not the output shaft, to the flat spot on the rear yoke where the strap bolts on and they figure from there.

If that yoke is indeed 6.5 inches it looks like you have about 5 of it exposed, too much IMO, especially if the first little bit of the splines inside have been machined down.

When measuring make sure you have the rear suspension loaded with full weight of the car on it, not hanging.

When it's all assembled and full weight on the suspension about 1 inch maybe just a smidge more OK, should be showing on that slip.

That may or may not be your problem, but the way it looks now if it's the short slip yoke would make me uncomfortable driving it. IF that thing blows apart and the shaft drops and hits the road , hang on. I had one let go on me about 35 years ago and it dug into the pavement and lifted the a$$ end of my car about three feet off the ground and set me sideways in the road, I was lucky it didn't roll.