I realize this is an old thread but I would like to update it as I just repaired a lower intake bypass pipe.

1st I first removed the old pipe and the piece left in the intake.

2nd Was to drill the hole with a 13/16" drill bit and chambered the leading edge with a 7/8" drill bit.(This was to make the lead in for the tap).

3rd Tap the hole with a 1/2" pipe tap. (I used 95% of the taps depth).

4th Assembled a 1 1/2"x1/2"NPT nipple into a 90* fitting and out of that with a 1/2"NPT x 3/4" barbed nipple.

5th Installed this assembly and the intake was fixed. (Now came the rest of the upper intake assembly).