What kind of SG is it?
If it is the Classic - which I suspect from your description of the neck - it would have the pickguard mounted pickups. If not, e.g., if it is a '50s Tribute, it will have the screw in mounting.
The problem here is that the BKP soapbar baseplates don't work with the pickguard mounting adapter used in the Classic and the other large pickguard SGs with soapbar P-90s. There are rivets right where the screws for the mount would go. You could contact BKP quickly and ask them if they would modify the baseplate to be like those in the Classics, or you could do what I did with my Junior - convert it to a screw into wood mounting.
If this is the case with your SG let me know and I can give you details on the mounting. If you go for the direct mount you might eventually want to change the pickguard as you would have four empty holes. Some pickguard manufacturers offer Classic pickguards with those holes deleted as this is a popular modification
EDIT: Oh, scratch that, I realize now that you have the '70s tribute with minis ... you will be fine. They have a plate in the bottom of each pickup cavity that works with either a mini hum or a screw in P-90 soapbar
You should see these in the bottoms of your pickup cavities. The P-90s screw into the two centre holes.
