The steering is different in between a walker and an STS. The walker has two steering cylinders and a tie rod in the back, while the STS has the center cylinder in the front of the rear axle. If the bolt pattern for the cam lobe motor yoke matches, the bracket to which the steering cylinder bolts, can probably be changed.
The hydraulic hoses to the hydrostat, where the four wheel drives t's in, will probably not interchange because of different lengths.