How to do modern interior window trim (extension jamb)?
If the look you want is modern trimless, be careful on how you remove the jamb extensions. It looks like the window jamb may go over the wood jamb extensions.
You will not need to add drywall to the returns. Add plywood instead, this way you can add 3/4&quot; 1/2&quot; or 1/4&quot; where needed and add shims if things are at an angle. Then add your corner bead to that, or even this...
Image courtesy Lowes
That way when the finished wood jamb is in place, the reveal, will be consistent all the way around and the dimension you wish to see.
When adding plywood or solid wood fillers you may need to keep it flush with the existing drywall to give either the corner bead or L bead some backing since it will be difficult to add a small sliver of drywall to the edge. It would be unnecessary to cut back the drywall, just to add more.
The L bead has a raised edge so the nail heads are below the raised edge so the nail heads do not get into the finish. This would all depend on what you have to work with. The standard corner bead may be the better choice.