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,