The LIU P/N 1180009L2 is a dual T1 module that supports dual timing. The LIU P/N 1180109L2 is a quad T1 module. Physically/Mechanically the units are swappable, but there are other factors such as software version of the SCU and LIUs that might be incompatible and cause a service outage on a working system. Hot swaps are supported if the units involved are the same P/N running the same software version i.e. like for like.
RG, you can check the software in the SCU and LIU's by navigating to menu item #1 - Configuration. The current System Release for the 1500 is 3.8, this should be reflected in the SCU configuration screen. The current SCU software is V15 with or without MLT. The current LIU software is T26D for the Dual LIU and T26Q for the Quad. Some changes in LIU provisioning may be required when moving from the Dual to the Quad due to system recognition. You will experience a short outage when you replace both LIU's assuming you're running redundant LIU's (A and B), as you cannot have a Dual and a Quad in the channel bank at the same time.