Just got back from the shop. They confirmed that it is the center bearing that is making the vibration, but that the flex disks are cracked. The quote for the driveshaft is almost $1100 and the flex disks are $310 each. Apparently the only center bearing they can find is from Dorman and that bearing only fits the Dorman replacement drive shaft and specifically mentions it will not fit OEM.

I am waiting to check with the owner to see if they will get the bearing and disks from Needswings, or the replacement kit from wholesale import parts. My feeling at this moment is that they don't want the hassle, so I will end up under the car in the driveway. Other than being a tad nervous at trying something I have never done before (not that big of a deal) I am more worried that I don't have a pit or proper car lift. I know you are supposed to have the car in neutral so you can rotate the shaft for bolt access. You are also supposed to torque the bolts down with the suspension under load. Trying to make that work with ramps and jack stands is making me feel like a contestant for this years Darwin award.

One more question for those of you with more experience at this than I have. Assuming this becomes a DIY job for me. I see 2 options:
Order center bearing ($99) and flex disks (2@ 99) from NeedsWings for $300
Get the whole replacement kit from WholesaleImport at $585

I can see benefits and drawbacks to each.