It took me forever to straighten everything out as to what would actually work correctly. There is a lot of information on what parts interchange, it mostly comes down to grease seals and bearings. Posting on the 356 forums was an exercise in crucifixion. I barely escaped with my hide. The Porsche-to-Beetle info is ancient, and the Porsche parts are too expensive to source while the Beetle-to-Porsche info is sacrilege and erased from the Gospel according to Rennlist.
HOWEVER . . . . on the A and Pre-A 356's, you can exchange the link and king pin spindle and entire brake assembly with one from a link and king pin Beetle.
This will give you cheapo Beetle front brakes which perform pretty much like the original Porsche units but cost almost nothing to buy new or rebuild and are available new on sale or used EVERYWHERE.
If you want to upgrade to discs, you'll need a set SPECIALLY made for the link and king pin Beetle. They're available here:
http://www2.cip1.com/ProductDetails.asp?ProductCode=C18%2D4202
or most of the other VW parts vendors on the web. Aircooled.Net offers a cheaper price, but their site is down for upgrading.
Not really that expensive, considering what's included and what the cost would be for a "rebuildable" set of 356C brakes. A rebuilt and working set would be WAY too costly for the average bear. The front discs only came on the last of the 356's and are a VERY desirable, genuine Porsche upgrade for the 356 crowd.
In my case, I'm just now having a pair of stock link and ling pin Beetle spindles cut flat and the bearing shaft and caliper bracket from a pair of Ghia ball joint spindles welded on in a dropped position. This will let me run Ghia rotors and calipers with a 2.5" drop on the front of my 356 bolted to the Porsche arms. The only thing that will need changing is the tie-rod ends to match the late model Ghia spindle arms.
So . . . maybe not as clear as I could be, but what you propose is Easy Peasy and MUCH cheaper than using Porsche parts. Even if you stay with the early Beetle drum brakes you'll be way ahead of the game and well satisfied.
Luck,
TC