eracode:

Fred99:

What's wrong with the existing garage door (apart from the way it's been built with the hinges and wheel brackets screwed in to what looks like timber mullions)?

You need a "decorative" timber jamb and lintel facing (the thing you've removed) flush with the interior lining / jib. A felt seal is stapled to that, so when the door closes it seals around the top and sides. 

Garage door suppliers will probably have a fit when they see what you've done - ie if they turn up and can't install the door.  They're also usually just subcontractors or on fixed rates per door, so good luck asking them for help fixing timberwork etc.  They'd usually get a builder in who knows what he's doing to sort it out, and expect it to be perfect/ready to go when they arrive.

That Builder's Bog will crack and probably fall out. 

Some of us have spent three pages of thread trying to impart that message. But it’s not getting through.

Oops - I’m supposed to be out.