proportioning valve question

[GoMangoBoys]

We are working on our brake lines right now.  I bought a whole set of lines from a company called Fine Lines.  They are literally 5 minutes from my house.  We are trying to hook it all up.  I have some questions.
1 What is the purpose of the second thing that looks like a distribution block that bolts to the proportioning valve?  There are enough connections on the proportioning valve to connect all the lines without the extra block.
2. In the attached picture, there is a plug in the top front position of the proportioning valve.  What is this plug and where do I get one?

[Dakota]

Just sent this to your phone:

1.  Metering valve

See description in screenshot below. 

[Chryco Psycho]

The 2 piece system was a 70 only  thing ,71up used a single unit .
The plug should be available from a store that sells all types of brass & steel fitting for industry ,

[Challenger in NC]

Brad, yesterday I was also working on plumbing up the lines and you can find the plug at an auto parts store like Advance or O'Reilly . I thought it was a 3/8" but that is too small, it is a size or two larger, I believe either 7/16" or 1/2". Can anyone confirm the correct size? They are about $3 each, I might just buy one of each size.