Hi Monoxide,
With the truss Dob you are thinking about, are you planning to build a Obsession-style truss or your own unique design? i.e. square mirror box or a round mirror box?
I may not be able to answer your question outright, but I am doing this same 'conversion' with my project
here. I have a BinTel 12" on order and I will be dropping in its GSO optics in my own truss Dob. Now I haven't seen a lot of the primary mirror cell in the GSO-style Dob's but I have taken the dimensions of the mirror and I made my own mirror cell. Fortunately I am able to weld so that helped. I chose to effectively start from scratch with the dimensioning and I used Kriege's Book as a reference. My mirror cell, and indeed the whole scope, will end up being a smaller version of the 'big Dobs' described in the book. Remember, when it comes to 'over-kill' and 'over-engineering' I am the King! The cell doesn't have to be as complicated as my one is.
Although I haven't yet reached half way, I am happy with my progress, and I can offer you measurements and dimensions of my work. I can also point you in the right direction regarding some of the 'custom made' items.