Cisco IOS sup-720 SNMP
In order to keep the same interfaces indexes, the only way to achieve that easily is moving the nvram:ifIndex-table from the old SUP to the new SUP.
This document says that the file can be downloaded and viewed:
http://www.cisco.com/c/en/us/support/docs/ip/simple-network-management-protocol-snmp/28420-ifIndex-Persistence.html
Procedure:
Old SUP:
#copy nvram:ifIndex-table disk0:
New SUP:
#delete nvram:ifIndex-table
#copy disk0:ifIndex-table nvram:
#reload