How to prep this old interior window lintel for painting

[Johnny Penstemon]

Hi all, the wooden lintel above the window in the pic was water damaged (long since dry) so I have removed the paint and cleaned. A few areas need wood filling but there are two things I don’t know how to do before redecorating:
1 The narrow facing edge needs to come up flush with the painted masonry above. It’s about 3mm shy. Not sure what product to use for this?
2 The underside is an uneven mix of the original wood and some old yellowed coating of something that won’t budge. What would you apply to smooth the entire area? I don’t think sanding will do it. I’m guessing a two-part wood filler isn’t the right thing?

Any advice gratefully received.

Many thanks, Johnny

 

[opps]

The gap between the header and plaster will always crack. I would pin and glue on a small timber moulding to bridge the gap.

You could backfill the header with 2 pack filler and then sand it flat, but it might quicker to cut something, eg 6mm MDF, to cover the header, in conjunction with the timber trim.

 

[Wayners]

I'd use a polymer grab and 6mm elements board.
3 screws through and some wall smoother or plaster over to cover.

Not got room for foil backed board or standard board.
Might have for 9.5mm plasterboard

 

[Johnny Penstemon]

Many thanks for the swift suggestions, appreciated. I’ll consider the options and go sort it. Cheers, J