You should have a vang not just for performance but for safety. You don't ever want the boom flying up, and that can happen with a sudden gust on a run.
A vang will come under considerable force and a pad eye on the mast or boom is not sufficient. You have a few options.
First, there is your current plan, a topping lift and a traditional rope vang. I am planning to remove my topping lift because it fouls in the top baton. Mine is just a wire that is shackled to the mast head and comes down to a fiddle block on the aft end of the boom. Others will suggest you rig a topping lift like a main halyard, meaning from the aft end of the boom, to the mast head, over a sheave, down into the mast, and out on to the deck and aft to the cockpit. They point out you now have a spare main halyard. Personally, I think that's just one extra piece of running rigging you don't need in the way.
As you thought, you'll need to through bolt a bail on both the boom and the mast, unless you have a deck plate below the mast step you can attach the vang to. Or, you'll need to do something very strong, but I doubt drilling and tapping will be strong enough. Maybe pop rivets, but I don't know. I'm sure you'll get many suggestions. If you buy an assembled vang from someone (Schafer, Harkin) they will tell you how to mount it.
Another option is boomkicker.com. This eliminates the topping lift by putting a springy rod under the boom and inside the vang. It will hold the boom up, and you pull it down with the vang. Pretty reasonable cost, but since you have no vang now I think there are better options.
Usually you don't see a ridged vang on a boat your size, but there is a company that will make you one:
Garhauer Marine Hardware -8892546
Garhauer Marine Hardware -8892547
That one is $330, which may be a good deal considering it means you won't need the vang or the topping lift. I would probably do this if I were in your situation, but maybe a better idea will be posted.