Typecast bytes in powershell

Question

In C, I have the following code

struct _file_header* file_header = (struct _file_header*)(cfg_bytes + (cfg_size - 16));

Which effectively fills the _file_header structure with the bytes from memory. I want to do the same thing in Powershell, but I am confused with the [System.Text.Encoding]::ASCII.GetBytes returning some bytes that aren't related to the data I see in cfg_bytes

Take the following PowerShell code,

$cfg_bytes   = (Get-Content $env:ProgramData'\config.bin' -Raw)
$cfg_size    = [System.Text.Encoding]::ASCI.GetByteCount($cfg_bytes)
$file_header = $cfg_bytes.Substring($cfg_size - 16, 16)

When I Write-Output [System.Text.Encoding]::ASCII.GetBytes($file_header), the output is not the same as I see from my debugger memory viewer. How can I obtain the bytes in the same format as the C example, such that I'd be able to read the same structure in PowerShell?