previous owner put in ipd poly engine mts.made the car shake so bad I put in orig rubber mts .smooth as silk now.But the rubber mts raised the engine and exhaust hits the body because of some weld work the prev owner did past the oxy sens.my mechanics suggested a custom exhaust vs orig starla etc.my question is stick with orig or go with custom

If you want a quick cheap fix while keeping the exhaust...
You might be able to lower the crossmember that the rear mount sits on a bit to compensate for the difference. 1/4” to 1/2” should do.
4 slightly longer bolts and some washers between the body and the crossmember.
$10 and 20 minutes or so.

Putting spacers to lower the rear transmission mount will affect the angle of the front driveshaft and could introduce vibrations. I read somewhere that driveshaft vibrations while accelerating was a common problem in some 240s even when they were new and installing spacers was a mitigation. My '90 240 has always had a slight vibration upon take off from a stop. When I replaced my trans mount a few years back I noticed that there was aluminum spacers installed on the cross member that led me to believe that they were installed to solve the vibration issue

good info....now have oem rubber mounts no shaking...the roof would shake,the rear view mirror would shake.I don't know why the former owner would put in poly IPD mounts...maybe cause he liked their products??

We are talking about the cat back part, right? (Resonator/muffler)? If the Starla vibrates, I would try another quality aftermarket cat back system. IPD used to make a one piece system. Maybe that would fit? BTW - Starla is aftermarket too. It is an OEM replacement. Volvo OEM is best quality but no longer available. Probably wouldn’t fit anyway....
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Will I buy another Volvo??? We'll see....