Alas, an angle grinder is a tool for which I do not have access. I have a Dremel and a Sawzall.

Also, any recommendations on a source for the geachange shaft assembly?

One site, BikeBandit lists it twice as such:

Triumph GEARCHANGE SHAFT ASSEMBLY

T1190850
$99.22

Triumph GEARCHANGE SHAFT ASSEMBLY

> Eng No 372712
T1190850
$99.22

What's with the "Eng No 372712"??