I had one of those braces on my 122 for years. It never ripped a hole in the fender, but it may have contributed to a stress fracture immediately underneath where it mounted. I can't say, because that's a known weak point on pre-'67 122s anyway (Volvo began reinforcing that area partway through the '67 model year).

I also have a minor concern that it might interfere with the engine exiting under the passenger compartment in a head-on crash, which was touted as an intentional safety feature back then. Happily, I never put it to the test.

But ther real point is... why would an engine need stabilizing? A well-tuned engine in good shape does not rock. That goes for high-performance engines too, even with big cams or whatever. All the stabilizer does is mask engine problems.