Well, it's apparent by now you are going to do this, despite good advice to farm it out for a one-time job.
So, I'll try to help you.
The way you break taps is:
1. Using low quality, cheap, or dull taps.
2. Getting them off-center with the hole and putting side force torque on them.
3. Letting chips build up between the flutes and bind up or gall in the hole.
4. Using no or poor quality thread cutting oil.
SO, some sort of guide or jig to keep the tap perfectly straight with the drilled hole is critical unless you have the skilled hands of an old machinist.
You don't yet, and tapping a few practice holes in mild steel won't give you some.
As for a jig and using the mount to align the holes?
A tap guide can be a complex as the $150 Williams jig.
Or as simple & cheap as a 1"x2" block of brass or steel bar stock with a clearance hole for the tap you can clamp to the mount to keep the tap straight with the hole while you crank on it.
Do-Drill is very good cutting oil. Get-sum.
http://www.brownells.com/.aspx/pid=1120/Product/UNIVERSAL-DO-DRILL
rc