disk swap bracket question

[paulbrgr9999]

How did you guys drill this hole in the firewall? (See pic.) Look closely and you can see the pencil mark I made where the hole needs to be. Sorry the pic is sideways.

I cant get a drill in that tight spot to drill a straight hole for the bolt that needs to come through and secure the bracket from the booster.

And drilling from the other side inside the cab makes me concerned that the hole will not be exactly in the right place.

thanks