Yeah, you'll need a monster air compressor to keep up with a blaster. I have a 4hp 20gal Campbell Hausfield and I don't think it would do it. Luckily, I have a friend with a machine shop that I can go to. It's only going to cost me the price of media. I bought some "Black Beauty" from Tractor Supply Company. It's crushed volcanic glass and cuts like a hot knife through butter!
I had to drill out the top bolts on mine too. The previous owner must have taken it apart at some point and put carriage bolts in instead of the correct counter sunk type.
Just center punch the head, and start with a small drill and work your way up. I think I went in with a 3/32" drill then an 1/8" and then maybe a #7. Something like that.
Try not to get too big or the 118* drill bit will mess up the 82* seat. If you can get down through the bolt, past the top, you might be able to grab the threads with Vise Grips and snap it off.
Can you tell I've broken a few bolts in my day?