I havnt done SCEA, but people tend to compare that to 483 (rather than 486).
I did not find 486 particularly hard, it requires logical thought rather than hard knowledge.
Basicly you need to read and understand
Larmans book.
Go to
ICE -- the questions are different, but similar, so you can get an idea -- whizlabs also do a test simulator which you may find helpful (at about 40 USD).
Good luck,
James