I think you need to supply more information about what you are asking, i.e.;
- Do you mean the front bumper, rear bumper or both?
I note that your car is a 260Z 2+2 - so we know that you need to use the appropriate rear bumper and brackets.
The only bumper conversion brackets I have heard of are those used to convert a US 260Z or 280Z from the bulky impact-absorbing bumpers (where each mounting assembly includes a shock absorber) to the 240Z bumpers with simple steel brackets, eg.:
MSA listing for front 'Bumper Conversion Brackets' - http://www.thezstore...n04a01i/32-1059
You should read this topic, which includes a dimensioned drawing of the standard (Australian market) bumper brackets supplied by Sirpent;
"Modified 240z front bumper brackets to fit a 260z"
Let me know if this what you are after, or if l have misunderstood you.