No Thuxton and TBS needles are different I didn't find it but there was a pic of the 3 next to each other posted once.

Yes a 40 pilot is possible but you would be going the wrong direction for your set up. Probably stay with the 42 unless you decide to remove or cut your air box.Just adjust the mixture screws. If you open up the intake some then might go to 45.130 main sounds close depending on your elevation for your set up. there again might have to go larger if you open up your intake more.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!