frame relay to atm conversion tool?

I'm trying to locate a tool (eg, spreadsheet) to convert throughput on a frame circuit to an ATM circuit. So, for example if you have a 512k CIR with burst to 1024k and 80% of the time you get your burst bandwidth and you want to convert that link to ATM, what corresponding SCR/PCR/MBS values would you need. I'm less concerned with Frame vs ATM protocol overhead than I am with calculating the difference in the way the burst bandwidth is meted out. Any recommendations? Supposing no one knows of such a tool. Would anyone be interesting in helping me put one together? Best Regards, -BM