Hi Gordanus... don't have a recommendation for you, but if the radiator is old, then the valves into the radiator are probably old too and may (should) need to be replaced, as closing the valves, opening the connections etc with the pipes / rad, may cause issues when connecting up everything once the job is done. If the valves do need to be replaced, then that is a bigger job as the system may need to be drained, and draining the heating system may have it's own "fun".
If not replacing the valves, it still may leak afterwards... please, once the job is completed, turn on the heating and leave run for few minutes... place some tissue paper under all the connection valves into the radiator - there should be no wet marks on the paper. Might just need another tiny tightening on some connection to resolve, but the person doing the work should do this before they leave. Be satisfied that there is no leak, no matter how small it may seem before you hand over money or that person leaves.
Don't want to frighten you, but just be aware that what seems like a simple job may turn into something bigger... best of luck with it...