通过直接读取PE(64位问题)确定dll是否为.valid CLR dll

我正在将32位web应用程序迁移到64位，并且我们的插件加载器代码有一些问题。

在32位版本中，我们扫描webapps bin目录中的所有.net dll，然后用Assembly.Load加载它们以检查是否存在我们的插件属性。

我们使用公共领域代码以一种相当漂亮的方式做到了这一点:

/// <summary>
/// Returns true if the file specified is a real CLR type, 
/// otherwise false is returned.
/// False is also returned in the case of an exception being caught
/// </summary>
/// <param name="file">A string representing the file to check for 
/// CLR validity</param>
/// <returns>True if the file specified is a real CLR type, 
/// otherwise false is returned.
/// False is also returned in the case of an exception being 
/// caught</returns>
public static bool IsDotNetAssembly(String file)
{   
    Stream fs = new FileStream(@file, FileMode.Open, FileAccess.Read);
    try
    {
        BinaryReader reader = new BinaryReader(fs);
        //PE Header starts @ 0x3C (60). Its a 4 byte header.
        fs.Position = 0x3C;
        uint peHeader = reader.ReadUInt32();
        //Moving to PE Header start location...
        fs.Position = peHeader;
        uint peHeaderSignature = reader.ReadUInt32();
        ushort machine = reader.ReadUInt16();
        ushort sections = reader.ReadUInt16();
        uint timestamp = reader.ReadUInt32();
        uint pSymbolTable = reader.ReadUInt32();
        uint noOfSymbol = reader.ReadUInt32();
        ushort optionalHeaderSize = reader.ReadUInt16();
        ushort characteristics = reader.ReadUInt16();
        // PE Optional Headers 
        // To go directly to the datadictionary, we'll increase the stream's current position to with 96 (0x60). 
        // 28 bytes for Standard fields
        // 68 bytes for NT-specific fields 
        // 128 bytes DataDictionary 
        //  DataDictionay has 16 directories
        //  8 bytes per directory (4 bytes RVA and 4 bytes of Size.) 
        // 15th directory consist of CLR header! (if its 0, it is not a CLR file )
        uint[] dataDictionaryRVA = new uint[16];
        uint[] dataDictionarySize = new uint[16];            
        ushort dataDictionaryStart = Convert.ToUInt16(Convert.ToUInt16(fs.Position) + 0x60);
        fs.Position = dataDictionaryStart;
        for (int i = 0; i < 15; i++)
        {
            dataDictionaryRVA[i] = reader.ReadUInt32();
            dataDictionarySize[i] = reader.ReadUInt32();
        }
        if (dataDictionaryRVA[14] == 0)
        {
            fs.Close();
            return false;
        }
        else
        {
            fs.Close();
            return true;
        }
    }
    catch (Exception)
    {
        return false;
    }
    finally
    {
        fs.Close();
    }
}

现在的问题是，我们现在必须处理64位或独立于平台的dll，并且偏移量似乎已经改变，这段代码失败了。有没有人知道对上述代码的正确修改以仅为有效的64位或独立于平台的dll返回true ?