I had a Scale Williams GG1 converted to TMCC, Lionel OEM Railsounds 5.0, ERR Cruise, LED lighting and Electrocouplers. The installation was done professionally by a Lionel Service Station. Total cost including the original cost of the engine $550. I have it listed for sale for $325 or best offer and there is no interest.
So, convert for your own use but don’t expect to get a premium if you decided to sell.