If I have both a brand new cam, and brand new lifters, does it matter if they’re the same manufacturer?

No, these parts can be (and often are) supplied from different manufacturers.
It is more important that the parts are from a high quality manufacturer.
Most SL6 camshaft "blanks" are still made in the USA so material and workmanship is pretty good.
"Made-in-China" lifters are getting more common and can be suspect.
DD

What I have are Melling lifters, and looking at a Comp Cams .220/.220

Why use an optimal-for-nothing camshaft from Comp Cams when, for less money, you can get something better for your combination from Oregon Cam Grinding or others?

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Joshua

consider Hughes Engines,

http://www.hughesengines.com/Index/index.php

when I spoke with them at the ICH Swap Meet they said they have many original Mopar cam profiles that
are designed to take advantage of the large diameter Mopar lifer. The story was they have additional grinds available
beyond the slant six cams shown on their web page.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8