Having heard some similar Sonys a long time ago now I'd guess they are reasonably capable. I think your problem is there is no demand for 1970s Sony speakers (or Sony speakers in general) excepting the real high end models and the market even for them is small. I think realistically you'd do well to get a ton for them even though I'd guess that they would compare favourably to anything new at under £500 at least.
Current Lash Up:
TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.