This is the official breaking in procedure according to the UK GR86 owner's manual posted elsewhere on this forum:
■New vehicle break-in driving (the
first 1600 km [1000 miles])
The performance and long life of your
vehicle are dependent on how you han-
dle and care for your vehicle while it is
new. Follow these instructions during
the first 1600 km (1000 miles):
●Do not race the engine. And do not
allow the engine speed to exceed
4000 rpm except in an emergency.
●Do not drive at one constant engine or
vehicle speed for a long time, either
fast or slow.
●Avoid starting suddenly and rapid
acceleration, except in an emergency.
●Avoid hard braking, except in an
emergency.
The same break-in procedures should
be applied to an overhauled engine,
newly mounted engine or when brake
pads or brake linings are replaced
with new ones.