Coal Fired Boiler Heatsink Radiator & Removing DHW Cylin

[HerefordHywel]

My parents have a coal fired parkray back boiler as their connected to a gravity fed system of 2x rads and DHW cylinder. They want to get oil fired CH but keep the coal fire if possible.

Would it be possible to remove the DHW cylinder from the current set up so that it could be heated by the Oil CH while leaving the two radiators on the gravity fed circuit to act as heat sinks?

The reason for this is because they could then carry on using their coal fire if wanted rather than having to remove everything (fire, boiler, pipework etc) and buy a new one without a boiler despite its probable rare use.

The current gravity fed set up is (from memory) diagram:

The proposed removal of the DHW cylinder from the system:

 

[Norcon]

What you want is a twin coil cylinder with nested coils and let both oil and solid fuel heat the cylinder.
A savvy plumber could probably set up a plate heat exchanger arrangement to re-heat direct from the oil boiler leaving the cylinder in place.