Weakest non magical being who can beat Silver Age Superman ?

The Blob.

If SA Superman struggles with a fat Lois, the Blob would crush him.

A fat woman is heavier then a fat man. FACT.

Ok, i think a well fed Galactus should beat S.A Superman without much problems. But dont have someone weaker than him who could do that ?

What about Wally Wast with no PIS ?

What about the KMC Trans tier list (excluding the magical ones)?

Amazo, Appolyon, The Asgardian Destroyer, Black Racer, Blackheart, Blaze, Count Abyss, Death Urge, Despero, The Doctor, Doomsday (H/P), Dr. Fate, Eclipso, Elders of the Universe (minus Ego), Fernus, Gog, Gray Man, High Evolutionary, Ion (current), Jenny Quantum, The Keeper, King Thor, Magus (original), Mangog, Mongul I (Pre Crisis), Nightmare, Onimar Synn, Onslaught, Queen of Fables, Resurrection Man 1 Million, Sentinel (Alan Scott), Silver Age Kryptonians/Daxamites, Solusandra, Stayne, Strange Visitor, Sun Eater, Superboy Prime, Superman 1 Million, Takion, Thanos, Tyrant (powered down), Validus

Silver Surfer 🙂

How ?

This really depends on portrayal. SA Superman had some crazy highs, but he also had some horrible lows. So it could be anyone from Spiderman (Peter) to Zeus.