Suppose we based everything on 'gG' and not 'c'?
For instance, all of Einstein's theories associated with relativity are based on 'c' being the founding universal constant. His 'thought experiments' were to illustrate that the 'speed of light' (actually, 'c' is not the 'speed of light', it is just a constant with the units 'distance/time') was constant across all 'relativistic frameworks', and the factors that determine the 'relativistic framework' are based on concepts of velocity, acceleration, and time. What would the theories look like if he had used 'gG' as the universal constant? That is, based all of our cosmological theories on the concept that 'gG' is absolutely constant no matter what the speed or velocity? But then, 'gG' is completely unrelated to 'time', so 'speed and velocity' have no bearing on it. They can not be the basis for a 'relativistic framework' for 'gG'. The constant 'gG' is all about force, distance, and mass, so those terms would have to define the 'relativistic framework' (note the absence of 'time'.)
Suppose the 'relativistic framework' was determined by gravity ('gG') and force, distance (space), and mass, not electromagnetic propagation ('c'), distance and time (speed and velocity)? Would not all of our 'modern' physics be based around gravity, instead of electromagnetic propagation? Would we not currently know much more about gravity than we now know? Perhaps we would not even be so hung up on our obsession with 'time' (since it has no influence on 'gG')? Einstein all but ignored gravity and the gravitational constant, somehow arguing that it was some artifact of space/time warping. Imagine the reverse - a construct of physics based on gravity ('gG') as the basis of force-distance/mass instead of 'c' for space/time, and assuming 'c' and time were an artifact of 'gG'?
Side bar, from the equation e=mc^2, the units of 'c' are derived to be m/s, distance/time, giving us the basis for describing the universe in terms of space/time. The units for 'gG' are force-distance/mass, no unit of time involved, a completely different concept of the universe.
So, given that we know so little about gravity, and 'gG', and our 'laws of Physics' are all constrained by our evolutionary predisposition to thinking in terms of linear 'cause and effect' instead of 'simultaneous probability' and the probabilistic nature of the universe, I can envision a species that had evolved differently than us, and whose brain structures were less linear (left-brained) and more wholistic (right brained). I can foresee that they would have a very different concept and perspective on 'Laws of Physics', unconstrained by our limitations and 'thinking style'.
So, a civilization that has evolved with a very different approach to thinking and to structuring the universe as they are living in and perceiving it, could easily be envisioned to have discovered a drive based on studying and mastering the principles of gravity, and the ability to focus and concentrate gravitational effects (waves? field? Boson?). With those 'black holes', there would be an abundance of 'fuel' for such a propulsion system, and a much greater compelling reason for them to study and harness it. They could, perhaps, investigate the 'laws pf physics' and the universe from a probabilistic and not a deterministic viewpoint, and consider quantum probabilistic non-time-dependent wholistic ideas of field theories and universal simultaneity instead of being hung up on time-dependent electromagnetic wave propagation and the concepts of time, speed, distance, velocity, and such.
Edited g to G