Compatible 904 trans donors

I'm not a 904 guru but I believe they upgraded a few pieces in 73 904's so a 73 or newer are the ones to look for. If you switch to a 727 you'll also have to change the driveshaft length and keep in mind that a 727 will suck 20-25 more hp to spin it's heavier internals so for the average street hp setup a 904 is the way to go. In the late 70's lockup 904's started appearing. They are weaker due to the input shaft being drilled to channel oil to the lockup part of the converter and performance converters are usually more expensive. You can identify them by the front 1/2" of the input shaft being turned down smooth where-as a non-lockup has splines all the way to the end of the shaft