I've never tried he car ride method, but just so you know I don't advise skipping the quarantine. The quarantine isn't just so the new chin doesn't have an illness that can pass on to your chin, it also allows the new chin to settle in to it's new home and for you to get to know it without another chin to deal with too. That being said, it's up to you how you want to do it. I've heard people have had great success with the car ride method when other methods to bond have failed. My only bonding experience was doing play times and slowing moving cages closer over time.
One thing to keep in mind though is not all chins get along, and just because they have lived peacefully with another chin before doesn't mean they will like a new one. The car ride basically goes on the idea that it's a stressful experience (in their minds) and that they live through it together so they have some common ground to bond from, like two people surviving a scary event together. I would still be prepared for them to need to live separate, if only for a little while. It really will depend on how they are in the car together, if they are squabbling then no putting them together right away could result in dead chins. I assume you've already read up on the car ride method so you would know more about it then me, but I've heard you want to make sure they are squished together, so they can't get away, or fight. Also make sure you have someone watching the carrier as you drive, so they can be separated if they do manage to fight.
My normal advice (since I've never tried doing a car ride) is to take it slow and let the chins tell you how to progress, if they hit it off right away, great they may be able to stay together right away. However if they don't you may need to take it more slowly and let them play over time before trying to put them together in one cage or maybe even repeat the car ride in a carrier to give them another stressful time to bond on. You also want to make sure you completely clean the cage they will be in so it doesn't smell like your existing chin and rearrange the cage too to avoid the old one feeling territorial. Play time in neutral ground is a good idea, let them play and bath together so they get use to each other, and with the bath, smell like each other.
