Manifold Radiator System

[crystal ball]

Looking at re vamping my old (40+ years old) system, a couple of rads have never worked properly & could do with another rad in the lounge, I intend re plumbing in Hep2o all going back to a 12 way manifold in the old airing cupboard, new flow & return from boiler (five year old Valiant),

Its a bungalow with good underfloor access, can anyone foresee any major snags?

 

[cross thread]

Just size the pipes correct and I can’t see a problem