FWIW, I'd take a look at the electronic e-units that folks like Dallee offer (with whom I have no relationship other than as a customer). For less than $50 you can get a 4 amp unit that handles either AC or DC. I haven't replace the e-unit on a 346 (but have on other locos where the e-unit is in the tender), but you should be able to either install it in the tender or perhaps even under the boiler shell in front of the motor. It also has the advantage that you can power an LED headlight from the board and it can be set to always start in the forward direction from a powered off position (e.g., block control). Dallee is at Dallee.com. If you plan on using the loco a lot - especially for switching - I think replacing the old electromechanical e-unit is worthwhile.