I forgot to mention that the 2650 already has a RAID 1 set for the OS which leaves 3 open slots.  Should I just leave those drives in place and install the other drives? 

The 1650 and the 2650 both use the PERC 3/Di, so it is possible, but things like differing firmware levels can affect how well this works.  If this is not critical - would just be nice - then it is definitely worth a try.  Power down, remove drives, boot to CTRL-A for PERC and clear the configuration, then  power down, put the 1650's drives in, power up.  It will tell you that a change has been detected.  Accept this and see if it boots.  Keep in mind, because of the differences in hardware, it may not boot or run properly, so you might consider installing an OS on a single drive to boot from and access the RAID 5 data from the single drive's OS.

if no important data present on existent HDDS and RAID not configured just remove them.

>>I forgot to mention that the 2650 already has a RAID 1 set for the OS which leaves 3 open slots.  Should I just leave those drives in place and install the other >>drives? 

try this

============================================================================

Importing or Clearing Foreign Configurations Using the VD Mgmt Menu

When a foreign configuration exists, the BIOS banner displays the message Foreign configuration(s) found on adapter. In addition, a foreign configuration, when present, appears on the right side of the VD Mgmt screen.

You can use the VD Mgmt menu to import the existing configuration to the RAID controller or clear the existing configuration to create a new one. You can also view the foreign drive data from the Foreign View tab without importing the configuration.

NOTE: The controller does not allow an import that results in more than 64 virtual disks.

Perform the following steps to import or clear foreign configurations.

2. During bootup, press when prompted by the BIOS banner.

The VD Mgmt screen appears by default.

2. On the VD Mgmt screen, highlight the Controller #.

The controller number is the only item that appears until you import the foreign configuration.

2. Press to display the available actions.
   
   
3. Press the right arrow key to display the available actions, Import and Clear.

NOTE: Ensure that your virtual disk has all the physical disks by verifying that there are no physical disks marked as Missing in the foreign view page and that all the disks appear as expected before importing them.

2. Select Import to import the foreign configuration or Clear to delete the foreign configuration and then press .

If you import the configuration, the VD Mgmt displays detailed configuration information. This includes information about the disk groups, virtual disks, physical disks, space allocation, and hot spares.

============================================================================

http://public.support.unisys.com/pcproducts/esx/docs/DellDocs5.4/en/Perc6i_6e/chapterg.htm#wp1066600

I stuck the drives in the remaining slot and powered the machine up.  The controller reported a foreign container, imported it, and the system came up.  The OS sees it as 2 drives like it was configured and all of the data is there. 

Thanks everyone for the input.

Yes, you can use the open slots without affecting the RAID 1.

Ignore Alex's comment, as it does not pertain to your systems or RAID controllers.

Good, glad to hear it :)