mikri,
The photo's in Stangers link are for a Series 1 Seven, which differs from the Series 2 & 3. The series 2 & 3 have a set up similar to the Cortina set-up in the other link. The issue with the Series 2/3 and Cortina set up is applying loads to the diff housing in a spot that has a sealing surface right above it. The casing will eventually distort and cause an oil leak, which then usually eats the rubber bushings. Using poly bushings sounds like a good idea, but they don't provide enough flex, and will speed up the distortion of the casing. A spherical bearing is a better solution. Here's a pic of my old Seven with the wide A-frame:
One thing to note with the a-frame set-up, if you choose to go this route, is to make sure the bracket welded to the axle casing is sturdy. Dear old dads Caterham had a bracket failure (luckily at the top of our street, and going about 5 mph) which allowed the axle to move rearward, pulling the driveshaft out of the gearbox (Ford 2000E). Had this happened at higher speeds, things could have gone very badly.
The Series 1 set-up was different in that the RH lower trailing arm was triangulated. It works well, but typically does require the use of rubber bushings to allow for some misalignment. Here's another pic, albeit from my old Eleven that used basically the same set up as the Series 1 Seven:
If I were to do it again, and not care about building a duplicate of a real Lotus, I would use a panhard rod. It's much simpler.
Rod