Whe hace 3/4" pipe thread nipples over here but they aren't tapered. Sure, they fit and would probably seal, at least with a thread sealant, but It would be kinda nice to have the correct thread. I don't want to crack the intake.
That may not work, if the tapered hole is larger than the thread for the nipples, they will go right through the bottom and not get tight.
Even with a tapered pipe thread and tapered pipe (plug) you have to watch how deep you tap the hole so it does not get too big and the nipple/plug won't tighten up and go right through.
When we did the drain plugs in the v-6 blocks, we used a straight pipe thread and a tapered pipe plug... That way the plug wedged its way down in the hole like a cork and sealed well...
Howeer most of the taps that you find here are all tapered... You need to go to an industrial tool supply store like Grainger or Production Tool Supply to find a straight pipe thread tap if you want to do it that way (the right way)...