The linkage jammed up on the new style switch. The switches are more different than you would think. From my experience & talking to a local tranny shop, the new switch does not work in the older tranny but it could just be my tranny.
There were different rooster combs used on the valve body and since that's what engages against the switch that's possibly the problem. I haven't worked on an older trans. than a 69 model since the 80's so I don't remember exactly what they were like. Also I haven't worked on very many 904's (mainly do 727's) so it's possible that the rooster comb on them is different. That said be careful when using a different switch than the original.