Nice score bigfella,
Angle grinder is the best option. Get a very thin cutting disc, suited for cutting stainless (I will post the part number tomorrow), anyway it's a very thin disc and cuts like a hot knife through butter on the keg. You'll be able to make a lovely clean cut with it. Draw the size hole that you want on the keg then folllow it around. I used one of those $20 angle grinders from Kmart and had the hole out in 10mins, clean, accurate and finished. Leave the handles (very handy) and cut the hole to suit a lid of you have one (aluminium wok lids work great, but wish I had a glass lid).
For the tap, I recommend drilling with a drill press and then welding a 1/2" coupling (stainless). If you have a Nubco or similar place near by this should cost about $5. If you don't have this option then drill a smaller hole and file out to the right size. You can make a bulk head fitting to suit (check the web for this) but you will need a length of 1/2" threaded shank. To this attach some washers (metal and rubber/silicone) and nuts. Then whack the ball valve on and your done.
It's very easy. Handy if you know someone with a TIG welder but if you were to pay someone to do it, it would cost bugger all. Great kettle in the end.
Cheers, JD
P.S. There is a squillion pages on how to do this on the net. Search around.
