Is it possible to preserve data on partitions while reinstalling Red Hat Enterprise Linux 6 using kickstart?

Issue

• The originally partitioned disks were created with the following configurations.

bootloader --location=mbr --driveorder=sda,sdb
clearpart --drives=sda --all --initlabel

part /boot --fstype=ext2 --size=150 --asprimary --ondrive=sda
part swap --size=4000 --asprimary --ondrive=sda
part / --fstype=ext4 --size=150000 --asprimary --ondrive=sda

part /data --size=1 --grow --fstype ext4 --ondrive=sda
part /fastdata --size=1 --grow --fstype xfs --ondrive=sdb

• This works great. However, when reinstallation is required on the host, it's required to preserve the data on /dev/sda3 (/data) and /dev/sdb (/fastdata) using the following partition scheme

bootloader --location=mbr
clearpart --none

part /boot --fstype=ext2 --asprimary --onpart=sda1
part swap --asprimary --onpart=sda2
part / --fstype=ext4 --asprimary --onpart=sda3

part /data --grow --fstype ext4 --onpart=sda4 --noformat
part /fastdata --grow --fstype xfs --onpart=sdb1 --noformat

• When using the above partitioning scheme, GRUB will try and boot from hd1 instead of hd0. Tried specifying the --driveorder=sda but the partition table is wiped out and onpart commands shows errors because they don't find the correct partition.