Since the intention is to use pitch change, not RPM, as the means of controlling the craft the response time will be faster. Therefore shorter moment arm lengths may be OK.
The actions of extension, rotation, pitch change and RPM should probably take place simultaneously. However, they may not take place at the same rate. Note that the PropRotor pitch and RPM changing are not a part of these mechanisms.
Gyroscopic Precession:
The gyroscopic precession generated by the tractor 'PropRotor and Motor Assembly' (PRAMA) will be opposed by the counter rotating pusher PRAMA on the same side of the craft. During hover (both axe of rotation are vertical) a very strong frame between the fore and aft PRAMAs will accept these forces. During cruise (both axe of rotation are longitudinal) a very strong frame between the fore and aft PRAMAs will accept these forces. During transition the rotation of the PRAMAs will probably be done slowly.
In other words these GP should not get beyond the tilting framework that holds the tractor and pusher PRAMAs.
I think ~ before thinking this through again. This should be a plus for having a closely coupled of the fore and aft RPAMAs.
Utilizing a motor that is not a slow-speed one and then utilizing a reduction that rotates the PropRotor in an opposite direction to that of the motor may keep the gyroscopic precession within the individual PRAMA.
A planetary gear could be used to keep the proprotor inline with the motor and reducer.
A higher speed motor will probably be a inboard one. This means a smaller diameter plus rigid outboard stator. This probably means that the transition mechanism can be lighter, plus narrower and thereby more aerodynamic.
Gyroscopic Moments on Structure:
Consider limiting the pilot's changing of the craft's attitude during the transition. At both 'ends' of the transition lock the proprotor-motor unit in position, so that much of the load is removed form the transition mechanisms and arms, or whatever. (such as the worms and wheels on Item 1611.)
Longitudinal Gap Between PropRotors:
Consider locating the motors inside the proprotor's hub, or even on the 'outside' of the hub. This will allow for an increased gap differential between the hover and the propulsion positions.
Downwash on Wing During Transition:
Consider having a leading portion of the wing rotate with the front proprotor and a trailing portion of the wing rotate with the aft proprotor. This will significantly reduce the chord of the wing at the location of the proprotors, however the moving portions of the wing will create some additional drag during hover. This idea will allow for a reduction in the longitudinal extension of this mechanism during hover, however the reduced gap between fore and aft proprotors may result in longitudinal stability.
