When I did my Beams conversion I kept my original brake booster and master cylinder, but soon after the swap I realised that the master cylinder was touching against the engine timing belt cover (mine's RHD remember).
It turned out that the brake booster and master cylinder combo from the ST202 Beams was way more compact than the one from my ST204, and this was the reason for the problem.
In the pic below, going from left to right you can see the red strut tower, the master cylinder and the black timing belt cover. It's not too clear in the pic, but the master cylinder and timing belt cover are pushed hard up against each other.

I didn't bother doing anything about it, but it has always been a concern that the pressure could be placing stress on the master cylinder, which could one day result in a braking failure.
Thankfully I grabbed all the parts from the clip before scrapping it, and yesterday I finally decided to have a crack at swapping everything over.
Basically everything had to be changed including the brake booster, master cylinder, ABS control box and all of the front brake lines. If I'd have done the swap whilst the engine was out (like I should have) the work would have been easy, but with the engine installed it was a bloody awful task!
Anyway it's all done now and everything seems to be working again. I was a little worried that the ABS control box thingy would be full of air and difficult to bleed after sitting in my shed for over six months, but after bleeding a few bottles of brake fluid through the system it seems to be all good.
I also finally installed the new tie rod ends that I bought back in September, but I can't yet tell if it has fixed the creaking noise problem. I'll head out for a proper drive tomorrow and see.
So the moral of the story is that if you're converting a RHD Celica to Beams power, make sure you have the thin brake booster, and make sure you do the swap BEFORE you put the engine back in!
This post has been edited by S8S8: Mar 3, 2012 - 3:24 AM