Re: Duality pickup size
If you buy a 7 string pickup set that is not in a soapbar size active mount, there are two options.
Make the route slightly larger at each end for the mounting ears then direct mount or add a pickup ring. To give the ring something to bite into you may need to use extra long screws or glue a dowel in each corner.
The other option is buy some cheap EMG style 4 string bass pickup covers then cut the mounting ears off the pickup baseplate. You’ll have to then trim the sides down and each end a little to get them under the cover. Probably a little hot glue on each side to hold it together.