Under BSD/OS 4.0.1 (maybe other versions too) you can dump an object file in 16 bit mode using the objdump command:

objdump -b a.out-i386-bsd -m i8086 filename

The trick is to get your data into some format that objdump can read. The easiest way to do this is to prepend an a.out header. Assuming you have a file with pure 8086 instructions (like bootany.sys), you can use the following program to prepend an a.out header:

main(int ac, char **av)
{
        char buf[1024*1024];
        static long x[8];
        int fd;

        if ((fd = open(av[1], 0)) < 0)
                err(1, "%s", av[1]);
        x[0] = 0407;
        x[1] = read(fd, buf, sizeof(buf));
        write(1, x, sizeof(x));
        write(1, buf, x[1]);
}

So, the steps are:

o Create a file, t.c, with the above program

o Compile the program: cc -o t t.c

o Create a a.out version of your file: ./t filename > filename.out

o Use the objdump program: objdump -d -b a.out-i386-bsd -m i8086 filename.out