5.x to 6.x or 7.x with 64MB /

[Nick Barnes]

I have a machine which I have recently upgraded using cvsup, from 4.x
to RELENG_5, as a staging post en route to 7.x.  The upgrade went well
until installworld ran out of disk on / and I realised it was only
64BMB.  My bad; should have checked before upgrading.  With help from
an on-site colleague the installworld was nursed to completion.  But
can I get the same machine up to 6.x or 7.x without repartitioning?
Advice please.

Partitions are as follows.

ad0     2439 M
ad0s1   2439 M
ad0s1a    64 M /
ad0s1b   128 M swap
ad0s1e  1024 M /var
ad0s1f   600 M /home
ad0s1g   623 M -
ad1    57259 M
ad1s1  57259 M
ad0s1a 10240 M /usr

It occurs to me that if ad0s1a is insufficient then I could use ad0s1g
as swap, and repurpose ad0s1b as a new /.  Is it straightforward to
installworld/mergemaster to somewhere other than / ?

Nick B