Retrofit wet UFH from underneath tiled suspended floor

[MattTheRobot]

Our kitchen floor is split between a suspended floor in the old part of the house and a solid floor in a new extension. The entire floor is ceramic tiled, on some kind of board backing in the old part. The old part is heated by a radiator, the new part by electric UFH.

I would like to retrofit wet UFH to the old floor using metal heat transfer plates whilst I am down there insulating. My questions:

1. Am I right in assuming that since the new part of the floor has electric UFH, the tile grout, adhesive etc used in the old part is likely to be the same and therefore UFH compatible?
2. Am I going to cause issues due to the heat warping the old boards, and if so will this affect the tiling, or should the layer between the tiles and boards keep this stable?

Attached is the only photo I can get of the construction, taken at a doorway.

Cheers!