If the motor mounts (2 ea.) and the rear transmission mount has not been changed in the last 100K then they are ALL well past their "normal" service life. The Volvo mounts used in these automobiles are FAMOUS for what most people would consider pre-mature death. Not a problem changing them (I own THREE of these things), just did the old yellow '86 245 for the second time. Just follow COMMON SENSE rules of supporting the engine-tranny combo whilst doing the repair. The tranny mount comes in two flavors, round or square, altough I have never had one that used the round mount. You cannot (emphasis on "cannot") tell if the tranny mount is good or bad via a simple quick look. You need to get a jack under the tranny (don't squash the pan) and raise it enough, gently, to see if the tranny mount really IS in one piece (you'll be able to actually SEE the two pieces of the mount once you get the weight of the machinery off of it). And, yes, this is MOST LIKELY the culprit when you have noise from the center bottom of the vehicle.
Just sayin'.

ASME, SAE