Master cylinder residual valves

[chewychevy67]

I just bought a disc brake kit for my 67 and I bought a master cylinder a long time ago for drum/drum when I was going that route. Now I just checked and neither side has a residual valve installed for drums when it was rebuilt. I have not used this yet. Can I use this cylinder for my disc/drum set up? Will having no residual valve in the back be an issue? Really not sure why they weren't I stalled in the rebuild. I will be using the disc combination valve.