Is changing the UCM Short to UCM Long possible?

[RetroOne]

Hi,
I currently own the two UCM shorts, one for the STECS system and one with the Gunfighter IV.

I am wondering if it is possible to only purchase the extended lower portion of the UCM Long separately rather than buying a complete separate UCM Long? I have the 100mm extension on the Gunfighter IV base and am looking to have it a bit lower.

Thanks in advance for any info you may have!

Regards,

Jim