I used to think I had a 240Z front bumper............. but the fittings on mine look different!
Anyway on mine it is 640mm between the two bolts.
View attachment 39325
that's a 73 late 240z bumper that use's the later bumper mount brackets that hold the bumper away from the body with a filler piece and rubber inserts on the corners,
Give me half and hour and I will measure mine now