I'm not too sure about unsprung weight and all the rest of it! I've just got an idea which will either work or wont work :S I'm just gonna build it, bolt it on an see. If it works.. great, if not.. so be it.
All i know is, I've designed the mech to give the same range of movement from the swingarm/shock as per the stock setup. I basically strapped down my rear end as much as i could (more than i expect i could get it to compress on the road), measured the angle change (swingarm) and the shock compression (mm) compared to its uncompressed/unweighted (riderless) state. I then set my solidworks model to the same 2 states and modified my mech untill i was getting the same amount of shock compression in both measured states.
I'm therefore hoping the bike wont handle much differently than what is does now. Actually, hopefully better with an upgraded shock!
With regards to the pivot point, yes il be pivoting on the r/h lower lug. I dont feel like this will need any further reinforcing. I say this because i feel like my subframe is strong enough to share the extra stress on the lug.
The entire mech will be made from aluminium except for bearings, nuts and bolts. The main arm will be 30mm thick (2 x 15mm bolted together) and the pivot plates (triangles) 12mm thick. All pivot points will be use a 10mm partially threaded bolt/axle. And all nuts will have a nyloc insert.