Universal brake booster 65 Cuda?

That won't fit your Mopar master cylinder, 2 bolt vs. four bolt.
Won't fit the newer aluminum 2 bolt Mopar master either, wrong bolt spacing.
Doctor Diff sells a good one, 7" diameter with the brackets if you order the A body version (will fit the early A even though it's listed for '67-'76). Not sure if it's currently in stock, my link to the site is acting up. Give him a call.
Very similar to what I run on my '66: a '67-'72 booster and linkage/brackets. Clears the valve cover, which the later larger diameter '73-'76 units will not. (Assuming you've got a V8, a slant 6 may not have that issue)