Removing wooden window surround

[Sparrowhawk]

I've started stripping back our bay window, which confirmed that the sides are open to the cavity. To insulate I need to remove these original wooden surrounds.

 

My first thought was a chisel in at the corner would split the plank away from the moulding but now I'm not sure I had pictured the construction correctly. I'm now thinking there is a 2x2" or 2x1" timber behind the plank that it's attached to, and the moulding facing the room is also attached to that?

 

What do you think the construction is and how would you go about taking this off?

 

There's 1+ coats of lead paint under the gloss, so I'm keen to keep sawing to a minimum.

 

 

Edited July 7, 2023 by Sparrowhawk