Drilling out sump plate holes ACCURATELY

Hi all,

I have a 1600 with some bad oil leaks around the studs which hold the sump plate to the bottom of the block. Some of them are quite loose and easily come out with only finger pressure, so I'm thinking I may have to drill/tap the holes out and get stepped studs, hopefully tightening everything up and stopping the leaks. While I'm in there I'd lock-tite the studs in as well.

First of all, does that sound like the right way to go?

Second, and more importantly, how do I go about drilling these holes out STRAIGHT?

The engine is in a Kombi so getting under it with a drill is not a problem, but keeping the drill straight so the holes don't end up cockeyed is what concerns me. Is there some kind of jig for a portable drill that could do the trick, or some other magic method that one can use?

Just thought of a third question: Are stepped studs a better way to go than helicoils?

Thanks in advance.