Hey Jevy,
Yes, I cut it with a hand grinder. I would say, use good quality cutting disks. I could quite literally watch the disk get smaller as I cut through!! Drilling, well use good bits (you will likely need a few) and a LOT of cutting lube. I highly recommend a drill press and a set of clamps too. It took me 30 min to drill out that cast iron, and it got SUPER hot. Mind you the bits were used, but the first one was near new and I still went through 3. lol
After I cut the end off the lunette, I test fit what was left into the tube, it wont fit. I flattened out the sides to slide in to the tube using a flap disk, worked excellent and fits super tight. Take your time to get it to fit in straight. Remember too, if you are going to weld it to the tube like I did, cast needs to be pre heated or it may crack (you probably know this, thought I would say it anyways).
Happy chopping!