Don't know what a commando engine is , but the Plymouth has her original Slant 6 ... As far as i know that was the first year of Chrysler slant 6.
As far as the caddy... I have had her for close to 8 years now. Been threw hell trying to get the 455 in her. I guess i have just had them to long. The plymouth is going on 11 years. Used to be my daily driver. I was planning on putting them both on e-bay come tax season any way.