For a long time, I’ve been using 8mm washers with a small outer diameter to adjust the exhaust pipe's height and balance its weight across the two rubber mounts; this also helps slightly reduce heat transfer. While it is possible to make thermal spacers to prevent heat transfer, they aren't really necessary. I’m still using the rear mounts from when the chassis was replaced at the factory in 2015; the front ones—replaced with mounts from a classic Mini—are about 5 or 6 years old and still in good condition. I once bought some blue silicone mounts that came apart when bent by hand, so they went straight in the trash without ever being installed. Normally, all TWs have the bodywork riveted to the chassis using 5mm stainless steel rivets (18mm long) with a synthetic fiber washer.
For the best performance and simplicity regarding the exhaust, the best approach is to have two 2.5-inch stainless steel pipes slightly bent and fit them with two TVR Cerbera track-day silencers. I’ve been running the unrestricted Morgan exhausts for five years now; they are a bit louder than the stock ones, but the performance is so good that you wouldn't want to put the originals back on—though there are likely still some left at the factory.
