Please help with the wrong booster from POL

[derotoreut]

I just received my 8-lug front disc conversion from Performance Online. The conversion was supposed to include a 11" single diaphragm booster, but came with a 8" dual booster. POL is telling me that the 8" dual will work fine and is better then the 11" single. Is this true? The information on page-29 of their catalog says, "not available in dual due to clearance issues" for the 67-72 trucks. I'm confused.

I am also wondering if they sent me the right master cylinder. Once I complete the conversion I will have a disc/drum set up. Is there a way to tell if I have the right master?

Also I have heard that it is better to have the larger 1-1/8" bore versus the 1" bore. How can I tell what I have if the master is already mounted on the booster?