I finally did the rollcenter conversion with my Mission and I used plates. I find that using the plates makes more since, here is my feelings on why I use plates.
1) I had a broken chassis....LOL...
2) raising the entire steering assembly places the steering tie-rods at parrallel with the ground while the car is setting at ride height..... reduces bump-steer
3) stronger----if a 2.5 mm chassis plte is strong a 5mm plate is stronger
Adrian, corner speed, muffin--- if you are concerned with changing the ackerman soo much, just remover the spacer from under the inner balls for the tie-rods and cut down the threads by about 2mm.... fixed
IMHO you should never modify your car in any way that will or potentially could weaken it... especially the chassis plate which is the most expensive and important piece on the car.