I've never had to use the restrictor on a 904 series but that doesn't mean your trans might not benefit from one. The number and rate of springs in the front servo also has an effect on the 1-2 and 2-3 shifts. The stiffer and more springs the softer the 1-2 shift and the quicker 2nd gear releases. If it only has 1 spring and it's not real stiff you'll get a good firm 2nd gear shift but it'll be slow coming off possibly creating overlap into 3rd