That's real odd. The only explanation I can come up with is your Banshee was built for a 20" motor. These motors were available from Mercury in 1959 and on.
What you need to do is remove your Thumb screws and replace them with engineered replacements, out of s/s threaded rod, having provision for the cup washer to fit on one end and a "milled hex end" at the other end. Note: The milled hex end must be small enough to pass through the cast transom bracket. I suggest the hex end to be milled to suit a SAE ring spanner. This will make it easy to turn is a small space cluttered by the front of your motor, steering gear and the sides of the well.
Here is a pic of what Mercury made in the 70's, for their 4 cyl 850. These were standard! https://www.ebay.com/itm/1440-6044A2-Transom-Clamp-Bracket-for-Mercury-850-4-Cyl-85-Hp-Outboard-1976-83/133022160928?epid=1534476072&hash=item1ef8bd1820:g:XvMAAOSwnJpcstO5
Note: One of these genuine Merc parts in the picture, won't fit your 700 (wrong diameter). This picture is just to give you an idea of what I'm proposing to assist you with your dilemma.
If that's too hard, there was a spacer available to turn your Merc into a 20" motor. It's called a pace maker (after market) and it fits between the gearcase and the mid section. You may be lucky enough to find one, but they would be like hens teeth now.
The last option as I see it, is to have your well modified to suit.