You ask a very good question. Though the 9N/2N and 8N engines are basically the same, it is the other parts that vary. All 9N, 2N, and early 8ns used the same front-mount distributor set up. The electrical systems changed from 9N/2N to the 8N so manuals will help determine what you have now and if 6v or12V needs to be looked at as well. 9N/2N models had a 3-speed tranny, 8N had a 4-speed and the I&T has Sherman info as well. You probably have a Step-Up, maybe a Hi-Lo Combo. Also, 9N/2N models only have DRAFT CONTROL built in, no side handle. The 8N would have POSITION CONTROL and the extra handle on RH side by the seat. These are the important things to know. My advice is to get as many manuals as you can, at least the I&T F-04 Manual, the 39-53 MPC, and the Operator/Service Manuals. You'll then have all the info on both for reference.