There are 2 different mainshafts used in 3 ribs. They both have 10 tooth first gears, but one has a bigger mainshaft that goes through the bearing under the nosecone. You could just measure the shaft, but if you take the nosecone off all you have to do is look at the shaft. The smaller shaft has a concave washer behind the snap ring..the "big" mainshaft does not. SO, if yours has the smaller mainshaft, then you can use parts from older "AH" code transmissions, but NOT the later "AT" and most single side cover car transmissions, because they have the bigger mainshaft. (Again, take the nosecone off of the car transmission and see what it has). If your 3-rib has the bigger mainshaft, you are in luck as then you can use the later style car trans components, especially 1st gear (it has 9 teeth.MUCH stronger them the 10 tooth). As for swapping both late and older car trans parts into a 3 rib, some things work, some dont, so it is easier to just match the car trans to whichever 3 rib you have. If you need any more help, just ask..
ericdebord@windstream.net Eric