Yeh i wanted to have some rake on the lower arms so the suspension will absorb some of the larger bumps instead of forcing the wheel back against the pivot axis, which would lead to premature failure.
Hope that sort of makes sense.
I also wanted the arms to be as long as possible with the pivots as close to center as possible. Keeping the angle of the arms at either end of these travel to as little as possible.
The whole sub frame has been reinforced with 5mm Plate. The caster rod supports and engine sub frame are joint with 30x3mm square tube and 40x4mm across the front. Used rose joints on all the pivots.