Doubt reagrding doa and cost indexing in capital gains

What is the date of acquisition of Capital Asset in case of an Industrial Plot ?

Year of Allotment from government : 2002
Lease deed executed in 2006.
And Payments are done on installment basis commencing in 2002 and ending in 2008.

Please suggest the treatment. What should be the date of acquisition ? How the indexation of cost will be done (whih is paid in instalments) ?