Hi Sam,
the requirement that you are saying, in this no enhancement is required.
open sale order value + bills to be cleared + value of open bills + Rs.60000
bills to be cleared and Value of open bills is one and same thing i guess.
So Sales Value already covers these forst 3 parts. next 60000, just increast the credit limit by 60000 of whatever you want to specify and its done.
In short you just need to increase the credit limit by 60000 and nothing else.
Regards,
Aayush Jain
SAP SD Consultant