Most 450s run 2/3 the way between 175 and 212.
Usually D-jet cars that are vapor locking are running too lean to begin with. Sometimes setting the fuel pressure a few pounds higher helps. VW had enough problems with vapor locking that they installed a blower that blew air across the outside of the injectors.
To be sure that vapor locking is the problem you can try jumping the fuel pump for about 20 seconds before you start. This will cool the fuel rail using the fuel as a coolant.
Bosch Master, ASE Master, L1
33 years MB technician