I did this a few months ago (well almost) but the question about moving the Master cylinder is yes, you can gently pull it forward and slightly toward the intake just a bit, enough to get the old booster out and the new booster in.
IME however it was also a very tight fit getting the booster in and out past the intake manifold (FZJ80).
My attempt failed however as I was out of town trying to do this in a hotel parking lot and could not get the four booster studs through the holes in the firewall by myself.
So assuming the brake booster and brake pedal bracket are similar in the FJ80 and the FZJ80, this is what I found:
The reason that the booster studs would not go through the firewall holes is due to the bracket for the brake pedal assembly/arm which bolts up to the cabin side of the firewall. It uses the same four holes as the brake booster studs so if those eight holes are not lined up it is impossible to get the booster studs through, IME.
The fix as mentioned above is to have someone inside the cabin pushing on the brake pedal bracket to keep the four holes in it lined up with the four holes in the firewall. That should allow the four studs on the brake booster to go through both the firewall and the bracket. It's a very tight fit for the studs, there's almost no slop between the booster studs and the holes in the firewall.
Having said all that and after watching the videos on you tubby myself, no one mentions what I found in their videos (having to line up the brake pedal bracket holes with the firewall holes). They either skip over that part or just wiggle the booster until they get lucky and studs go through, likely because their brake pedal bracket is still lined up with the holes in the firewall and didn't slip out of place when the booster was removed.
FWIW
