Is this correct rocker configuration 273

Agreed if the rockers were modified accordingly and ideally the shafts had an extra oiling hole for pressurized oil to squirt onto the valve stem.
I interpreted the opening statement of adding 273 rockers to a 340 to mean they were stock 273 rockers. If these are indeed stock rocker arms it would be beneficial to ensure the rocker and shaft oiling holes are clear of debris.