3.1 lock to lock seems to be a speculation, factory info states 3.5 lock to lock. Have now had a quick look in two books with GTV tests and 98% state 3.5 lock to lock, in a couple of test they write 3.7 and 3.6, which probably is misprint or wrong info. The tests contain both LHD and RHD cars.
Tuners of the time however offered faster steering by 28%, either as rebuild kit or complete unit.