Query regarding zerodha margin benefit in nifty short straddle

Need to know if I can sell 1 lots each of OTM CE and PE as MIS so margin blocked would be around 70k for each contract (if for NRML it’s 140k each contract), then can I convert it to NRML if margin calculator (ex opstra) says margin required for this short straddle position is 140k (hence margin benefit)?

Yes, you can take a position in MIS and later convert it to NRML, you’ll get the margin benefit after converting your positions. You can easily check the margin requirements here.