Get someone qualified to inspect the work that was done; there might be an issue that either didn't get fixed or wasn't fixed properly. What you describe could be quite a number of things and without driving your car it's very hard to even point you in the right direction but it sounds like something is seriously loose or shifting. Who did the work?

To be safe I wouldn't drive the car until you find the problem. To compare, my '69 tracks dead straight at any speed up to and well beyond highway speed; yours should too.