Removing Decals from 1970's Plastic Train

I am looking for suggestions on how to remove dried on decals from plastic toys from the 1970's. I acquired bits and pieces of a Timpo Prairie Rocket train set and I'd like to remove the decals before painting the cars in a more realistic style. I tried soaking the cars in warm soapy water for 24 hours and no luck. Also tried a product called Goof Off which is basically acetone and it started melting the plastic. Any suggestions greatly appreciated!

Thanks!

Nick Stern