A standard bit should do it. I don't believe the screws are anything special.
Have you tried an impact driver on it? If you're going to drill it anyhow, nothing to lose if you knack the slot up with an impact.
Merely altered, not made. Disliked that bog standard grey junction box they used on the chipper, so replaced it with a smaller, black inline junction box, (& dropped one of the case screws down the blade area whilst I was at it :whistle:). Cut the top gland off & capped it with a plastic cap...
@Theblackbox
Check these bolts are tight on the exhaust shields. I spent nigh on a hour searching for one yesterday, when they vibrated loose. 8mm head.