some news about the woodruff key?
I don't have an old Gilera, so no experience with that.
But aAs far as i remember a woodruf fkey is something which has the shape of half a circle.
The slot in the shaft als has this shape.
So there should be no problem with slipping away keys while mounting the ignition plate.
As you have told about height, width and lenght it may be that you have a simple square key.
This one should fit very tight to the slut in the shaft.
Otherwise it could fell off or slip away.
So maybe you should filea new one which fit only with some 'force' into the slut.
Or try to get something to buy.
The width is easy to measure with a gauge at the slut in the shaft.
The length should be somehow the same as your plate.
The height could be measured with the plat mounted on the shaft.
There should be some gap on the upper side between the key and the slut in the plate.
Maybe you should look after metrik keys instead of ANSI ones
Gilera is a european brand, so no americna stuff
Searching for 'DIN 6885 Passfedern Form B' maybe a point to start
<edit> uupss.... no 2,5mm x 3mm available?
Could it be a 'real' woodruff key?
2,5mm x 3,7mm x 9,66mm?
Scheibenfeder DIN 6888