I would recommend getting the carb from Stovebolt, I made the mistake of actually finding a 5200 from a '74 MII 2.8L V6 and then rebuilding it and it cost the same amount.. (live and learn).
The Stovebolt adapter really isnt bad, it just wasn't designed with Mustangs in mind. Remember he sells Ch*vy performance upgrades and it is a minor miracle that it even fits on our fords. To aid in the installation Tom also sells a "partial linkage kit" for 5$ that includes a replacement linkage arm, and a longer shaft to go between the original throttle rod and the new carb linkage arm. There have been several articles written about installing the carbs and adapters by members of this forum (even me, if I ever get the darn thing installed)
by Ducktang
http://www.geocities.com/dualsprings/ducktangpage2.html
by Falcon62 (comparing the Stovebolt vs the Clifford)
http://home.centurytel.net/fordfan/Falcon/HW Conversion.html
by me
http://phlegm.us/FordSix/tech/Induction/stovebolt/stovebolt.html
The problem with the stove bolt that most report is inadequate hood clearance for a "real" air filter. Some have claimed that a chevette or early pinto has a really low air filter unit that will work for you, but I have not been able to locate one.
Other Options:
I found this 2 pics on this forum a while back
And it got me to thinking "How hard could it be to build my own?". So I started work on on that, to get the lowest one possible that will cost me less then the clifford but fit better then the stovebolt.
http://phlegm.us/FordSix/tech/Induction/Carb_Adapt/DIY/Make_Your_Own.html
As you can see I have the general layout that I want figured out, and hopefully next week I will get my brother-in-law to mill me one out of a 1" thick peice of aluminum.
I will keep updating my DIY page till I get one that I like
good luck, and have fun
ron