Square bore to not so spread bore?

You can or used to can get square bore adaptors that had the 4 holes and would allow you to rig the thing to fit the wide/ narrow bolt pattern. They normally came with special shallow head bolts that went into hex holes in the bottom of the adapter, to stick up into the carb. If you find one used, you can make those bolts by grinding the heads a little bit on common 5/16 bolts.

The mount holes are set up similar to the adapter in your photo, only the throat bores got straight through