Is it O.K. to use the 7.0 ports tree on 6.3 ?

[Pete French]

I have a set of machines running 7.0 and a set running 6.3 which I
would like to use the same ports on. I was under the impression that
there was only one ports tree, so is it safe to simply untar the
ports.tgz file from 7.0 on the 6.3 machines, rename INDEX-7 to INDEX-6
and install away, or are there more subtle differences to tran the unwary ?

cheers,

-pcf.