'half a block away' is correct and usable in written English.
You can use it to describe the physical distance between two points. For example: "The restaurant is only half a block away from the park."
They found an empty garage half a block away.
He landed in a tree half a block away, lucky to be alive.
He comes from his apartment half a block away once a week to clean the shrine.
Watching from a street corner a half a block away was Ms. Gagliardi.
Within weeks, a comparable penthouse half a block away was listed for $900,000 more.
"Isn't she kind of cool, in her little hippie top?" he asks, eyeing a woman half a block away.
"Everything was great, until this came," said Ms. Rios, pointing to the power plant half a block away.
This is due largely to the huge street traffic our temporary location presents but also to Blick Art's presence half a block away.
She ended up about a half a block away, in front of a florist shop at McGraw Avenue and White Plains Road.
In recent days, the police have tightened restrictions to keep the protesters at least a half a block away from the mayor.
The button man, meanwhile, had moved to a phone bank half a block away.
