Hey there,The one I have is this one from GIVI Outback 58L Top case. It can hold two full size helmets, the case is big and quite suites the size of ST.Here are some pics https://goo.gl/photos/EqsjqXFEnJeDtTAm6.
This thing is humongous - and even if that is a sturdy Aluminum rack, the fact that the mounting point on the frame is basically under the front edge of the case makes me shiver. The stress on the mounting points must be enormous.
There are 4 mounting points on the frame with M8 bolts through Ř18 and Ř22 tall spacers.The load should not exceed 13lbs (6kg).You can judge the mounting pattern by this instructions sheet https://www.yumpu.com/xx/document/view/49822823/sra2101-kra2101-givi
I got the 42L version of the Givi trekker outback because you can't open the lids of the oem yamaha sidecans with the bigger top box. I have had 2 other monokey top boxes(one a 52L) and no problems with the mounting system. If someone has broken the front tabs it would be nice to know.
I don't think you can open some close fitting, top opening panniers with that box in place, I know my OEM panniers would not open with a similar shaped 46L Givi from my ST1300 that I was hoping to use. Ended up with the narrower 42L Outback case instead.