[TUHS] v6tar from v7 on v6, too large?

[Will Senn]

All,

According to "Setting Up Unix - Seventh Edition", by Haley and Ritchie:

The best way to convert file systems from 6th edition (V6) to 7th 
edition (V7) format is to use tar(1). However, a special version of tar 
must be prepared to run on V6.

The document goes on to describe a reasonable method to make v6tar on v7 
and copy the binary over to the v6 system. I successfully built the 
v6tar binary, which will execute in the v7 environment. I then moved it 
over to the v6 system and did a byte compare on the file using od to 
dump the octal bytes and then comparing them to the v7 version. The 
match was perfect.

The problem is this, when I attempt to execute the v6tar binary on the 
v6 system (it works in v7) it errors out:
v6tar
v6tar: too large

on the v7 system, it works:
v6tar
tar: usage  tar -{txru}[cvfblm] [tapefile] [blocksize] file1 file2...

I don't think the binary is too large, is is only 18148 bytes.
ls -l v6tar
-rwxrwxrwx  1 root    18148 Oct 10 14:09 v6tar

Help. First, what does too large mean? Second, does this sound familiar 
to anyone? etc.

Thanks,

Will