Infinity g1310a parameters needed

Hi,
My friend bought this driver on ebay and now we are planning to do a sub for him. Unfortunately we don't have all parameters (actually we miss xmax) and we are not sure if the data we got are correct. We couldn't find this speaker on the internet.
That's all we have:
8 Ohm
pe 180 Watt
fs 23 Hz
spl (1W/1m) 87 dB
Re 7,6 Ohm
Le 4,26 mH
Mms114 g
Vas 61 L
Qes 0,329
Qms 9,219
Qts 0,317
As I said we miss xmax the most, is it any way to measure that?
Maybe you know some sources where I can ask.

Thank for your help.