Apologies, you’re referring to the second picture. I think that looks far too small for a soil pipe based on the image. However as you postulated previously, the property was (possibly), highly deficient in build quality so it may be wise to take precautions. What is the width of the pipe imaged in the second picture? Is it possible to refer to US building regulations for the necessary width of soil pipes for that era, in order to confirm accurately so you don’t cover your face in faeces?