Removing the shell and installing a printed board over the motor ***'y. A 30 volt with a 2 amp rating power supply to run multiple engines. A hand held remote to operate the PC board circuit i n the engine . The PC board may have a mini speaker, hook-up for front and rear lights, whistle, bells, and engine noise thru the speaker. This I have operated from other peoples set-ups.
Converting locos usually isn't that hard. The worst situations happen trying to isolate the motor from the frame but even that isn't too difficult with experience. I've even installed DCC into a Bachmann 4-8-4 Class "J", which has split frame construction that directly contacts the motor without too much difficulty.