Start with a test on the Fuel Shut-Off. VERY simple. COSTS NOTHING (always start with the option which gives you the most information with the least investment of time, energy and money).

Motor Mounts may well need to be replaced, but they are not the most likely culprit in the shutdown/shaking scenario.

Trace the brown vac. line coming off of the unit (Fueal Shut-Off Valve) at the firewall end of the Injection Pump. Pull this line from the junction at the other end (bunch of vac. lines meet next to brake booster).
Is there oil in this line (a sure sign of Fuel Shut-Off Valve failure as oil is being vacuumed from the Injection Pump Rack through the Shut-Off Valve diaphram and into the vac. line)
Apply vac. pressure to the line while the car is running. How is the shutdown?
Apply vac. presure while car is not running. Does the unit hold presure or does the pressure leak out? If there is pressure leaking out then diaphram is leaking and unit has to be replaced.

Once you've tested this Shut-Off Valve you will have spent a very few minutes and no money and you will know whether to replace the part or move on to further diagnosis.