Read up on the FDISK command in DOSBOOK
http://www.drdos.net/documentation/qkstart/05ugch5.htm
Instructions for 7.02 but 7.03 shouldn't differ that much I'd imagine
http://www.drdos.net/documentation/usergeng/28ugbapp.htm
Just don't put in the partition size and you should get prompted for a start and finish cylinder.
Doesn't 7.03 install over the top of 5 at all using existing the existing partitioning scheme? It shouldn't refuse to install like MS Dos does but may give a notice to update an existing system using the INSTALL command at the dos prompt. Also saves the existing setup if you want to back out at some stage in the future.
Right well armed with the User Guide I've made a bit of progress.
DRDOS 7.03 does allow you to specify start & end cylinders for the primary partition (you need to leave partition size blank to then be asked for cyl refs)
BTW there is an extended/advanced form of DRDOS FDISK which is invoked by FDISK /X - this provides extra features for FAT32 and non-DOS partitions
After setting the primary partition parms, FDISK automatically proceeds to format it.
This process was completed without problems so I then transferred the OS files with "SYS c:"
This also seemed to complete without problem, although command.com wasn't transferred and had to be copied separately.
On reboot, OS stopped loading after showing ~"Share should be loaded for big drives" and the system froze.
Setting up a share entry in autoexec.bat made no difference.
Also tried FDISK with 5.00 and SYS with 7.03 - froze on boot as above.
So, I think there must be a significant architectural difference between DRDOS 5.00 and 7.03.
Primary partition starting at cylinder 1 works for DRDOS 5.0, but not for DRDOS 7.03.