You will need more that 2 CLs. The more the merrier. But to be honest CLs will out grow a 29 gallon pretty quickly. I would say leave out the CLs and add a few different gouramis. May be a couple of dwarf qourami.
CL's can get over 10 inches, but that's in years and years of growth.. You'll probably end up stunting them in a small tank, I would suggest not putting them in. You can get smaller loaches, maybe a few yoyo loach