Excerpts from netbsd: 13-Feb-98 Changing the NetBSD partiti..
"Robert.V.Baron"@gluck.c (5609)

> Below I have
> included patches that let 0xa3 (163) be the "prefered" partition for
> NetBSD 1.3.  The booter and label code search first for a 163 paritition
> and then if they fail, for a 165 partition.

I have similar patches in the queue for at least half a year,
most work was done by Duncan McEwan.
(They use ID 164. Is there a specific reason for your "163"?)
In an article I picked up somewhere ("How it Works -- Partition Tables"
by Hale Landis) both 163 and 164 are marked as "reserved".
160, 162 and 167..176 are eg "available".
It's more a political issue than a technical.

best regards
Matthias