Reassembling a trailer from original 5.1 stems is a unique challenge, especially when you're more accustomed to stereo mixes so I don't think there is a way to make this process faster. I haven't tried to reassemble a truck, but I often get all the equipment and trucks from this second-hand marketplace for my construction business:
https://www.boomandbucket.com/equipment/trucks. Besides the products they have, they might also help with vehicle reassembly. It could be a real time-saver and help you avoid damages during the process.