From what I have been able to find on IRS it appears as if everybodies design is different.
Has anybody got a upright design that :-
1) is strong
2) Light
3) Can be manufactured at home
4) Has all the brackets for calipers
5) has been proven.

Then one can start playing with the arm lay-out.

I've drawn up a complete IRS for the Locost, but I just need to tidy it all up and make it presentable.
The upright is a very simple affair and can be assembled from mild steel sheet and bits of RHS.
It's not of much help to you now, but I'll post it as soon as I have it ready.

Please U2U me when you post it, in case I miss it.