Dual boot FreeBSD 4.10 and FreeBSD 5.3

[Kjell B.]

I'm about to make the switch from 4.10 to 5.3. However, I don't want to 
do it in one go, but rather first install 5.3 on a separate physical 
disk and get all applications installed and configured correctly. Once 
I've completed the process, the scenario is a RAID-1 setup (gmirror is 
the route I've chosen after extensive reading).

Current situation
-----------------

  [homebell] ~> uname -a
FreeBSD homebell.dyndns.org 4.10-RELEASE-p2 FreeBSD 4.10-RELEASE-p2 #0: 
Mon Oct 18 21:48:34 CEST 2004 
homebell at homebell.dyndns.org:/usr/obj/usr/src/sys/HOMEBELLapmipfw  i386

  [homebell] ~> df -h
Filesystem    Size   Used  Avail Capacity  Mounted on
/dev/ad4s1a   126M    66M    50M    57%    /
/dev/ad5s1e   252M    64M   168M    28%    /rootback
/dev/ad5s1f   150G    28G   110G    20%    /backup
/dev/ad4s1f   252M    90K   232M     0%    /tmp
/dev/ad4s1g   112G   9.8G    93G    10%    /usr
/dev/ad4s1e   252M   123M   108M    53%    /var
procfs        4.0K   4.0K     0B   100%    /proc

  [homebell] ~# atacontrol list
ATA channel 0:
     Master: acd0 <COMPAQ DVD-ROM GD-2500/0011> ATA/ATAPI rev 0
     Slave:  acd1 <Hewlett-Packard CD-Writer cd16n/1.15> ATA/ATAPI rev 0
ATA channel 1:
     Master:      no device present
     Slave:       no device present
ATA channel 2:
     Master:  ad4 <HDS722512VLAT80/V33OA60A> ATA/ATAPI rev 6
     Slave:   ad5 <HDS722516VLAT80/V34OA6EA> ATA/ATAPI rev 6
ATA channel 3:
     Master:  ad6 <HDS722512VLAT80/V33OA6EA> ATA/ATAPI rev 6
     Slave:       no device present

ATA channels 2 and 3 are on a Promise TX2 ATA133 controller. ATA channel 
1 on the motherboard is fried and unused.

ad4 hosts my 4.10 installation, ad5 is a pure backup disk, and ad6 is 
today empty and it's where I will put 5.3 (ad4 will be the mirror to ad6 
once the migration is completed).

Therefore, I first want to install 5.3 on ad6 (actually ad6s1 I believe) 
and dual boot between ad4s1(4.10) and ad6s1(5.3) during the migration phase.

I'm a bit uncertain as to the procedure to get to the dual boot status. 
Currently, I have no boot manager installed. Can I install 5.3 onto 
ad6s1 and from sysinstall install the FreeBSD Boot Manager to both ad4 
and ad6? Or should I first do 'fdisk -B -b /boot/boot0 ad4' from within 
4.10 (as per the handbook)? Or is 'boot0cfg -B ad4' the proper way of 
doing it?

My concern is of course to not mess up my current 4.10 installation.

-- 
Kjell