This is out of the question because it would have to destroy the glass cloth and epoxy. The fin box could not be installed because the structure is closed.
Speed with one T200 is here T200 on fishing SUP - #16 by e-sup
I don’t know the expected speed with 2 x T200.
More essential than speed is the ability to drive straight and an electronic anchor. Whether this is possible remains to be seen.
I will write about electronics here SUP with electronic stearing - #4 by Alex_M - Rover 4.0 - ArduPilot Discourse