You should decide whether you're going for the concours look, and must restrict to OEM type looks, or if you want the latest in High-Tech, oil platform protectants. There is at least one word you need to fe familiar with.
As I have mentioned earlier in this manual, you should spray or paint a layer of zinc over all the welds and gaps, and inbetween the panels. All the holes and gaps accesibble should be the target of your spray can.
I know it ain't cheap, but at this stage of your restoration, choosing the right stuff is essential for your long time value of your soon to be restored 356. When you (and the wallet) feels like the car has gotten enough of the precious metal, it is time to order some real rust inhibitors, like Por-15, RustMort, Corroless and similar expensive but very good products.
I especially treated the longitudinals with layers of zinc, followed by Corroless, and asphalt mass, on top of that i put a coat of low gloss or matte black paint. After the longitudinal was sealed I drilled out a hole from the inner longitudinal (actually 3 holes to reach all areas) and inserted a tube with special nozzle to spray a coating of non drying seed-oil. (Dinitrol product)
Trond Vidar Olsen