I don't think this applies - especially Black Legion - that is units from the host codex. The problem is that the Primary is entirely proxies/counts-as and the secondary is the actual codex. So me as an opponent look across and see a sea of green - but some aren't greenskins, they are humans. Not the same.
I really like this army. But having played the poor fella with Raven Wg, made to get a SM codex just because the units were painted white scars - he was forced to proxy a speeder as a LR FFS - you will be fighting an uphill struggle. I know, why not have an amry using these models - as orks. No allies no fannying around, orks. Solves all your problems of whether or not you get an army done in time.