Can I fit a modern radiator to a gravity fed radiator?

[Jock Spanners]

Evening All,
I turned up to change a radiator last week only to find an ancient rad connected to a big old steel one pipe system with no return. Is it possible to connect a modern rad and valves? Would I need to pipe it top to bottom? There's copper tails coming off the steel pipe tees.
Thanks,
Jock

 

[ShaunCorbs]

Manual rad valves eg no trv unless it’s suitable for one pipe danfoss make them

And yes tboe is a must