In case you were considering it don't try to press the inner tube out whilst the s/a is still in the frame, I tried this and belled out the frame plates
.
The tube is usually rusted to the bushes and is COMPLETELY immovable.
So its best to cut the inner tube and use the methods in the posts above or elsewhere (I think i posted a while back on doing this job, in some details with pics).
I do not have a press, once the old blocs were out I pressed the new one's in using 16mm threaded bar.