The OEM rack "How To" thread doesn't match the 2017 EX

[pekingduck]

Honda has changed racks for the CB1100 several times without explanation. It looks like you have a rack for a 2013-2014 bike. It has a spacing of around 180mm, where your bike needs 200mm. Your front mount will be fine with the right bolts and spacers.

Some of the 2014 racks from Honda came with an adaptor plate to use on the DLX models, but while its spacing is wrong for your needs (and you can't order them either), the illustration gives you an idea what you will need to make.

There is an unused hole on either side at about 160mm, but there is just enough room behind it for a nut, so you will have to fit the right length bolt. Basically you'll need to put a spacer over that hole so it is level with the rear mount, bolt a strap across it, and drill a hole in the strap between for the rack at 180mm.