MK IV tubular spaceframe drawing

Yes, the construction of my chassis is somewhat different to yours, monocoque central tub with low mounted front and rear subframes, and no roll cage. I would think that the roll cage could easily add 5cm or more to the front CoG vertical location
 

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Interesting construction, very interesting! I don't think the roll bar has that much influence on the GC. It weighs about 17kg which is less than 2% of the total weight.
 
Yes but it's impact on the CoG location must be multiplied by it's own CoG location distance from the mass centroid; i.e. a 17kg that is 70cm above the centroid will have 10 times the impact of a mass that's 7cm above the mass centroid.
 
Just looking at your rear suspension geometry (first 2 attachments in your last post), I was trying to figure out how your arrange for mounting the bottom of the rear shock works. Is it a type of U-shaped bracket that is jointed at both ends (lower control arm and lower shock mounting)? Or is it a fixed (not rotatable) joint between the top of the bracket and the bottom of the shock?
 
I might have spotted a potential problem area (or it just isn't visible in the photos)
The top ball joint in the front suspension upright is bolted directly to the upright.
This will probably cause binding when suspension travels up (bump) Would need a raised surface or spacer underneath the mounting surface there.
 
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