A 3 inch notch in a 4 inch beam which supports a lot of floor and a wall?

http://www.dicegeorge.com/psb/psimg/...otched167m.jpg

There is no wall underneath it.
How to strengthen it?
I was thinking of replacing the floorboard with a length of steel,
maybe an L shape with notches where the rafters are?
Screwing it down with coachbolts?
Its a flying freehold, underneath is a friendly neighbour,
with a posh ceiling.

[g]