Note that LAPACK isn't four decades old (and probably should be superseded anyway). You perhaps won't want to use large-scale numerical libraries that are that old unless they've had a lot of development and been well parallelized.

One issue with mixed language programming that we learned decades ago is the issue of debugging that there typically is across the interface. Also general tool support. I recently asked the local Python expert about HPC-style profiling of Python calling C(++) libraries, for instance. (I couldn't make TAU work.)