Help! More brake questions

[thunderbolt]

I will preface by saying I am sure about this.
Isn't the disk brake master cylinder larger than the drum brake one and hence pumps more volume. If you use the disk brake master cylinder then I think you should get the disk brake proportioning valve otherwise increaced fluid volume will only make the rear drums lock sooner. Maybe you could get and adjustable proportioning valve (I would but you may not be comfortable with one of these) and then dial in the correct proportioning yourself and not worry about right valve with right master cylinder.
Of course as I said earlier, I don't know any of this for fact.