How big a job is replacing this lintel with a concrete one?

[jheyds]

Hi, I'm after some advice regarding this wooden lintel, it's a victorian terrace house.
I want to replace the doors and windows, and whilst doing It i was thinking it would be a good idea to address the rotting lintel.

If anyone has delt with similar i would be interested in any info they could share, ie cost, time frame, how it's done ect.
Many thanks
James

 

[Wayners]

I've seen those wooden lintel taken out and concrete lintel placed in.
You can use slate to pack
Lime mortar in.

 

[crank39]

Might be better on the building section seeing as window and door guys don't usually get involved with removing lintels