[Ant]

I personally think solid mounting isnt the way to go, solid mounting is a quick way for some people who havent got the time or whatever to design a proper mount!
I know a guy who rebuilds very valuable classic racecars and he said they are high maintainance with everything designed light and rigid, and parts do fatigue more often due to the stresses and limited miles they do, but they are race cars and solid mounting can give quicker lap times, and as Colin Chapman said as long as they break after the finish line!

My engine uses a sleeve welded to the engine bracket 1/4" thick steel cutout , I use poly flange type bushes, that have a metal sleeve pressed into them for the 1/2" mounting bolt, and engine plates attached to the chromemoly chassis upright, this setup has some compliance and there is no detectable movement, the same with the sidepipes the rubber type mount needs to be designed so it actually supports the muffler etc, so it might be better to have it under compression.

Mounting an exhaust solid is okay if the engine doesnt move, but on race cars they are often held on lightish supporting brackest with a spring or suchlike holding them to the bracket so they can move a bit with flex or heat change. My experience with solid mounting the mufflers resulted in a cracked exhaust manifold.