I’d just drill it with a 17mm, the tolerances don’t have to be close
I started with that idea and then thought;
1) I’d have to buy a 17mm drill bit anyway (probably a blacksmith’s bit as I only have a 13mm chuck) so cost is no different.
2) I wouldn’t be certain I’d got it central in the existing hole, even using the pillar drill, and I’d worry about it ‘catching’ and taking a chunk out as I’m only trying to increase the hole size by a little and then it woudl be ruined internally.
it really only does need increasing by half a mm or so.
I’ve got 6 of the parts to do in total.