Threads screwed on gearbox

[snapetwo]

So I bit the bullet, pulled my suspension AGAIN. swapped the s6 K out for the v8 k...
Well bone head me, didn't bother to check the threads on the gearbox.2 of the 3 will thread, top one will not.
What are the fixes that anyone has used?
I don't have a tap that fits, if i gotta buy one I will.
WIll this work? or do i gotta look more at maybe cutting a hole and welding in a nut?

any advice or past experience would help.
thanks.

 

[67Dart273]

Taps aren't all that expensive, I would think that's all you'd need.