3400 is probably close to right. You might drop to a combination of the 2400 and 3400 before going all the way to 2400. You can mix the springs. You test for total advance with vacuum not hooked up. This way you can get the total mechanical for WOT set(should be 34-36). So at 3400RPM with no vacuum advance hooked up, in the drive way, you should see around 36 degrees when the engine is at 3400 RPM.
Once you have total set, you can lock the distributor. No go for a test drive with vacuum hooked up. If you dont get any pinging, you can take it back home and change the springs. Drive it again and see how it acts. Once you start hearing a little pinging on part throttle acceleration, go back up to the previous springs and you are good to go. I suggested the mixing, because 2400 is a little early and 3400 is a little late on some engines. It really can be different from engine to engine so you just have to try it.