No problems with the mounting, there should be no flexing, all of the pressure is fore/aft. If it can stand up to many years of racing including several 12 hour endurance races, hauling that car down from 145 mph, the street should be no problem.
Great pictures. After doing the upgrade did you notice any problem with flexing of the caliper spindle mount, they seem so small compared to the Volvo mounts. Were you able to retain the stock Jensen wheels.
I am debating on whether to go with the Volvo or the Toyota 4Runner (and Cressida rotor) options for the front, in all cases the caliper bolt holes have to be bushed and redrilled to the corect 3.5" spacing.