Probably easier to hack saw than drill. All new chains I've purchased in the past several years come with the new style master link that works with a shifty bike. Caveat that I've only bought 9 and 10 speed chains, but either should work with a 5 speed freewheel. So no extra cost.
When you see the new master, it will be clear why this works, and the old retaining clip type doesn't. I happen to carry a spare (along with a breaker) in case I break one on the road. Hasn't happened to me personally, but I was able to help out a fellow on a group ride who broke his chain. Interestingly, my master was a 9 speed, his bike (and presumably chain) was a 7, and it worked. So not a lot of difference there.