Here's what I did. I cut the top off of all three. As far as how to cut the tops off, there are numerous methods. I opted for an angle grinder and a cutting wheel. I had no trouble whatsoever making nice round openings. I just layed the guard on the grinder against the keg for support. As far as getting your fittings installed in the kegs, i had mine welded but the weldless fittings are another very good option also. To make life easier i put a combination sightglass/thermometer on my Hot Liquor Tank which holds your strike/sparge water. Also a 1/2 inch stainless ball valve. My boil kettle only has a ball valve. The third keg is still not being used. I use a 10 gallon round rubbermaid cooler as a mash tun. The cooler mash tuns will hold temps much better than a keg. I do plan on eventually going to a HERMS setup which will utilize the keg/mashtun but until then, the cooler rocks. Hope this helps, this forum is your friend as well as youtube
I got fittings and such here
brewhardware.com