Hi Riley,
With a surface piercing drive, the stuffing tube sticks out of the transom between 10 and 13% of the hull length, in your case 6 - 7.8 cm.
The angle of the propshaft must be as shallow as possible, usually meaning a very long propshaft, or a flexshaft.
Too steep will lead to a catastrophic running attitude.
As an example the business end of one of my monohulls, a 63 cm boat with a 32 cm long propshaft.
Your shafts are short(ish) with only 25,5 cm between the motorflange and the rear bearing (I have two of these shafts).
The motor has to sit as low in the hull as possible, no Chinese iron angle, but a proper motor bulkhead, which allows the motor to almost touch the bottom.
When the boat sits on a flat surface, the rear bearing has to be about 2 mm above that flat surface:
Ignore the position of the rudderblade, that has to sit next to the prop on a monohull, see my first picture.
As your motor will have to slide back 6-7 cm, the propshaft angle will be too steep, and you'll need to drill new holes in the transom and bulkhead.
As you'll have two rudders (or none and steer with the props via a mixer function) I'd position them behind the props, this means a longer outholder for the rudders.
To be honest, I'm not comfortable with the flat bottomed hulls without any curving up at the bow, my guess is you'll be in for a very 'adventurous' running attitude, to put it mildly...
The two long bolts that come with these stuffing tubes are there because these shafts also live in the boats build by Dragon, which are powered by outrunners and cooled by an extra water cooled spacer (also available at HK), 9 mm thick, with a 10 mm hole in the middle for the solid coupler and the shaft.
As that the motorflange only allows for a Ø9,5 mm coupler, the hole is Ø10 mm, you'll understand these shafts didn't last long in my boats and were replaced by standard size motorflanges and propshafts, with standard size couplers.
Here the stock shaft with an aftermarket inrunner, notice the extreme close fit of the stock coupler:
And the new, longer propshaft with the stock outrunner on a home made watercooler:
I'm not sure if this is going to work, I already pointed out that the motors chosen aren't very suitable.
These revs are intended for a fast electric, not a fast moving camera platform with flat sponsons.
Running at partial throttle a lot, risks overheating both motor and ESC.
Regards, Jan.