what size rotors are they using? (will they fit under you rim size 13",14",15",16")
How far out are the calipers going to stick? (Bassically what offset rim will you need to clear them.)
These are the questions you need to ask the people doing the work for you.
If they fit, then no, its not to big, its never overkill with brakes, the bigger the better.
Hope it works for you.
The other problem may rise in the AE86 stub axles, which are fairly small, and may bend or break with excessive force.