In reconsidering how this drone is going to move, I have come up with a different idea. Eight BLDCs is a lot of weight, and four coaxial sets means four ports in the airframe; that is a lot of lost wing area, and therefore lift.
The new idea is to make the VTOL component more like a bi-copter, using two coaxial pairs of drive units. These components will be in two ports. A third single drive unit will be mount rear and center. This unit will have the tilt component and be located just off the extreme back end of the airframe.
On vertical liftoff, the bicopter pair will provide the bulk of lifting thrust while the lone unit at the back will be pointed vertically groundward and provide only levelling stability.
At a predetermined altitude, the lone unit tilts in steps to provide pushing thrust until forward flight is established. At this point, the lifting coaxial pairs disengage. The ports through the airframe would then be covered, either with a sliding door, or a hinged door attached fore-ward.
Control of forward flight will be maintained through a combined aileron/flap actuated by servos.