No driveshaft weights are somewhat common so no big deal there.
Runout will tell you if your driveshaft is straight.
Use a magnet and set up a wire pointer that's close to the middle of the driveshaft about 1/8" - 1/4" away.
Assuming you don't have a locker diff, get one tire off the ground - safely blocked, jackstand etc. - trans in neutral if a stick shift and spin the wheel by hand while you watch the driveshaft.
The distance between pointer and driveshaft shouldn't change to any great degree as the driveshaft revolves.
If I remember right the max allowable runout is 1/16".

If you have questions, pull the shaft and take it to a driveshaft shop where they have a driveshaft balancer.
Most cities have a driveshaft shop.

I've had some shafts require balance weights and some that do not.

If runout is excessive, most times the driveshaft shop can bring it into compliance . . . and if it needs balancing, they can do that as well.

If the driveshaft checks out, take the rear wheel/tire combo to a shop with electronic balancer and see what's needed.

I have 285/70R x 15 BFG tires on 10" x 15" wheels and they balance just fine with stick-on weights in the middle.

There's a chance the shop you were at did a static balance due to the large tires.
If so, go to a shop that sells 4 x 4 tires and they'll be able to balance your roadsters tires.

Double check your motor mounts to make sure one of them isn't loose.
Your difference in uphill/downhill vibration could be due to that.

Another one is to check the driveshaft angle at trans and diff.

As far as smooth idle goes, any chance you have #5 & #7 plug wires running parallel to one another for an overly long distance?
If so, one will induce a voltage in the other and fire when it shouldn't.

Along those same lines, are you sure the plug wire firing order arrangement is correct?


The taking the car out of gear and coasting will tell you several things.
One of them being the plug wire bit.