I might just try the inside mount first before you bother bending it.
And, yes, you pretty much just bolt the strut on there and try shifting to the smallest cog to see if there is any interference.
Not sure what "orthodox" is, but 175mm to the outside of the bosses sure isn't typical! In this case, with the spacing and unique configuration at the rear axle it almost seems like the designer intended the rack to be inside mounted. The only drawback is slightly-inconvenient access to the fastener. Luckily you don't need to take racks off that often.