I don't see a reason why you couldn't use a RLL in a Colt LE901. The 901 uses the same fire control geometry, buffer tube and stock, control layout, as well takes a standard AR15 5.56 upper should you wish to.
Ultimately, the LE901 is nothing more than an AR15 with a 308 sized mag well.
If you can use an HK Sear in a HK23e or a DIAS in a AR47, AR45, or MGI Modular lower I don't see how a LE901 is that much different and is ultimately mechanically less different to a stock AR15 than an semi auto HK "E" xport version belt fed is from its 5.56 mag fed variant.
I have personally never seen a letter stating that a RLL cant be used in an AR10 either. I believe a DIAS is more mechanically problematic in a AR10 due to the bigger rear lug and the sear trip geometry is higher up than an AR15. (and which is easily rememdied on a RLL by using a taller paddle)