The builds are different in that Martin set out with a clear plan on what he wanted to build from a fresh shell, as dont forget his car was to replace the one he rolled on the gumball, so had done a lot of his learning on that, where as Rod's car has evolved over time, so a lot of items on Martins car were right first time in one build based on what he knew he wanted from his experience with the other car, where as many things on Rod's car will have gone through various evolutions over the years.

I guess if Rod ever crashes his car and starts from scratch with a new shell as a result, that his build then would need to be done more like martins this time to get it all turned around in one go.