I did mine with a little right angle Phillips with no problems.

 

 

Yep, similar to above. I got a long, thin, right angle ratcheting driver set to do it after getting fed up singing my hand using a shorter right angle screwdriver. Cost me $20.

 

No point in buying what's after all a fairly standard tool from Triumph, they don't make it and simply add a mark-up, (66% in this case).

For example I have the Carbtune one, it's a quality right-angle geared driver, very useful for all sorts of jobs: synchronising, reaching awkward mixture screws etc, and costs £44 (USD62):

http://www.carbtune.co.uk/bevel.html

There's also the Motion Pro one at $77:

https://www.motionpro.com/product/08-0229

 

I just did this and used a small 3/8 drive ratchet with a Phillips head bit. Worked great.

 

I noticed this in classifieds, but maybe you need a Phillips head?

http://www.triumphrat.net/for-sale-wanted-gear/693378-throttle-body-balancing-tool.html

 

but maybe you need a Phillips head?

That tool looks like very good value. I don't think it matters what bit you have. The screw head is shaped to accept both a normal slotted or cross-point bit, this sort of thing:

 

I and my wallet thank you, all! ?

 

I did it with the cheap first pic type screwdriver. Been sitting in my tool box for like 200 yrs. Finally found a use for it. Only had to do it once in 30k miles so far.