Great write up and pictorial!

I had to make this same emergency repair a few years ago when, on Memorial DAY, of all times (when NOTHING is open), I sheared ofmy key trying to spin the engine briefly to make sure the timimg belt was loped through correctly. ?this was a step in my Bently manual. I didn't have the crank bolt tight so......

After a few minutes of panic and an urgent apeal to the Brickboard for any local member to help me by provifding a spare gear(Balu Vandor did reply, but after I solved things), I though about what I was facing here.

Realizing what that key does (spot your alignment of the gear-to-crank pulley) and what is doesn't do (take lateral force) I figured there was no lateral stress on it once the crank bolt was tightened.

My solution, of course, was the same as yours. Drill out the broken key and insert something to peg the aligment of the gear and pulley.It's just an alignment item, not a structural thing.

ONly difference in appraoches is, I used a small bolt which I screwed intothe new hole I drilled. then I used my air cut off disc to remove the bolt head and give the needed length to the peg.

Been working great now for more than two years.
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"Can't understand why people abort Volvos, either"