Personally, I would talk to your local DMV folks rather than getting opinions here. Every state probably has somewhat different rules.
Do you have a clean title to the 54? If so, the DMV doesn't care what you do to that vehicle; new engine, replace half the frame with an IFS, or even a different frame. As far as the DMV is concerned the 54 is still the same vehicle with the same title.
When you say you are going to "move the Vin over to just the body" what exactly do you mean? If you mean you want to remove the vin tag from the S-10, I'd reconsider. That is a felony in most places and will really cause a problem with the 54's title.
