Forget the backspacing. Stock montero offset is +10 mm, changing it to +15 mm is just fine if you plan to stay with close to stock tire sizes 31-32" if more you might start having issues. Although it would still prob fit 33s fine. One disadvantage going to 17" wheels tires will cost noticeably more. Then there is that center bore issue.

92 SR, 285/75R16 Yoko MT ARB locker GAST compressor AirLift 1000 MM10500 Snorkel custom rear bumper
02 Montero LS died protecting the master
08 PowerWagon (stock!)