I don't want to be a wet blanket but making the "wedge" is the easy part.
The real problem will come when you need to redesign the azimuth (RA) and altitude (Dec) bearings. The Azm pivot is designed just to keep the "rocker box" central on the base. It will not form a stable pivot once you put a radial load on it.
I once modified a Dobsonian mount to make the azm a substantial bearing with a new pivot that had thrust races to draw the two sections together firmly and ball race wheels replacing the three teflon rub pads. This made a very rigid assembly for driving with a geared stepper motor and belt. However if mounted as an equatorial platform the flexure of the rocker box was a still problem.
The Declination bearing will present another problem. The existing arrangement won't be very suitable. You will need to make a proper bearing that will hold the optical tube and allow it to move at least from pointing at the pole up to the equatorial plane.
As a digressing here you have given me a couple of ideas. I have a LX200 10" classic set of forks or a LX 6 set of forks here that I could use to hold an 8" F4 dobsonian without too much trouble and mount it on a wedge like in your picture.
These forks have the gear drives and I have a set of electronics that will fit the LX200. It would be an interesting project even if not very practical as I would expect my HEQ5 pro to be a better proposition for photography.
You will find information on my modified dobsonian here:
http://barry.sarcasmogerdes.com/obse...s/DOBMOUNT.DOC
Barry