Tapping inlet elbow

[Eeyore]

Hello! I got a cheap die and tapping set off ebay. I now have two thingies to put in the manifold for the boost pipe but both are too big for my tapping set. Any ideas? B&Q didnt have any tappers at all!

Also what are peoples opinions on drilling the elbow on the car if i do it carefully with a sharp drill bit? and how hard is it to remove?

Boost gauge is sorted now. Just litterally need to connect it to the manifold!

Thanks
Sam