A bent wheel will be immediately obvious when they go to balance the tires. Ask them to look for that though, so the guy is aware that it's a possibility. If these are trhe 16-inch "Hydra" wheels, they are unlikely to have survived this long without SOME minor bend somewhere along the way. If it's not too bad and doesn't make the tire out-of-round, have them balanced and try it out. If there's one bent a little, have it mounted to the rear and start looking for a spare.
I just replaced a severely out-of-round tire on my wife's 740... a 14" tire but somehow became almost D-shaped. We suspect a radial belt shifted or came apart internally. Gave a low-speed "wobble" in the wheel, and something of a high-speed vibration. Actually got better up to about 60 mph and then worse.

HOwever, your problem is also just as likely to be bad brake rotors, and I think you may find that they are badly warped. Happens to a lot of 740s, especially when they have bad cone (control arm) bushings. Since you've fixed one thing, now fix the other.
Good luck!
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Rob Bareiss, New London CT ::: "Roterande Fläkt Och Drivremmar!"