Thanks, helicopter-redeye - this system looks nicely automated:
http://www.e-equipments.com/vibrex2000.htm
Some interesting discussions going on here about instrumentation techniques.
MJB, regarding cabin size increase the CG will have been carefully calculated. This machine will have been designed as a prototype using the R66 powertrain, but adapted to an R44 testbed. You will probably find that that the prototype has been massed up to replicated the likely R66 weight (depending on test requirement). This just allows the design engineers to gain confidence in their components/systems, by accumulating some hours before the proper R66 airframe is tested.
I imagine there was a detailed R66 concept evaluation before even starting the powertrain evaluation prototype design. Most likely RHC have done extensive wind tunnel or CFD work and have a very good idea of drag coefficients and cruising speed. I would have though they opted for 3 in the back as a good packaging compromise. From memory a "tadpole" shape with 2.4:1 length:width offers the lowest fuselage Cd. Once the flight testing has proven out the R66 powertrain, you will likely see a prototype with the intended R66 fuselage.
Doing it in small stages is the sign of a well run test/development program...