I agree with Shawnboy about your rotors. 10 to 1 odds that your front rotors need machining. If you ignore the problem it won't be long before you notice the same thing happening at slower speeds and by then you'll have to replace the rotors.......
The same thing happened to me with my 84. I ignored the high speed shimmy, and when it started happening at slower speeds(like when coming to a stop) I had to replace the rotors because they had become too thin to machine.
<font color=blue> WE WILL NEVER SURRENDER<font color=blue>