Details on the 3400c can be inferred from here:
http://mywebpages.comcast.net/macdan/images/pb3400resistors.jpg
It shows configurations for 4.5x, 5x, and 6x multiplication ratios. The bus speed is controlled directly by the crystal. Although I don't know for a fact that there's no other way to change bus speed, I strongly suspect that changing the crystal itself is the only method, as ratios close to 1:1 are inconveniently generated.