Donor for 63 dart GT

Stock should be a 903 transmission. 1st gear not synchronized. Probably the weakest of all the Mopar transmissions. Manual transmission cars generally came with a lower gear ratio in the rear end than an automatic. There should be a tag on it showing what it is unless someone took it off and didn't put it back on. You can pull the cover and look on the ring gear too. There's also a way to spin one axle shaft and count the revolutions of the drive shaft.