Hi @[FC-T] Kinsler24445
Yes you are allowed to use parts from one truck on another truck, as long as the switch complies whit rule 3.3
§3.3 - Floating and clipping parts*
It is not permitted to use parts which float from the truck or trailer, such as floating cargo models (even if only one object in the model is floating). It is not permitted to use any parts which cause models to clip through each other, such as a cargo model which clips through the truck cab - minor clipping such as between the parts of a hybrid truck are permitted.
But how minor clippings is defined, it's up to the Game moderator to decide