Depending whether it is steam or a hot water system on the type materials you should use.
You also have to consider Cast Iron is a very compatible for heating applications as it holds the heat much longer then a copper counter part with no creeping sounds as it expands and contracts.
You also have to size the new radiation according the EDR and heat loss calculations of the new type of “rads” compared to the ones your replacing.
If you send me an E mail I can have a GREAT Long Island Master plumber contact you for the installation of the correct sizing and product.
Most unemployable helpers (apprentices) and other non licensed individuals who do not know codes are now getting into the heating fields unfortunately.
I would strongly suggest you hire a licensed Master plumber rather then taking a chance with your investment to a Fly By Night (FBN).