Hi Zapp, a Rayburn is placed in situ in one piece as apposed to an Aga which is built in position.
A general heating engineer can connect it all up as with any other gas boiler following installation instructions which are mostly available online.
I might be useful to look for independent Aga/Rayburn engineers in the area though as you will no doubt need one for service/repairs in the future.
If you know of the model of Rayburn you are interested in i can advise further on reliabilty and availability of spares etc.
Quite happy to advise by pm if you prefer.👍