ORIGINAL: Barry_G
I've often considered building one of these myself.
My idea was to use a couple of ball bearing drawer slides and build a simple rolling platform to bolt the engine mount on. Then use a digital fish scale. I'd build in a locking mechanism for starting and adjustments, then have a release allowing only limited movement (matching the linear distance spec. of the scale) to safely take the thrust measurements.
Your idea is good, but I would question the integrity of the drawer rollers because of the engine vibration.
I'll post pictures this afternoon of the mock up
Roger