I've got a '67 with J56 Brakes but I'm wondering if I'm missing the backing plates or if they never had them to begin with. I don't believe the JL8 front plates will work.

Here is a link to my page:

http://sciflyer.0catch.com/DiscBrakes/DB.html

Appreciate any info!

Did you get it backwards? Don't you mean use J56 plates on a Jl8 setup?

J56 used plates, Repro JL8 plates are available I think, but expensive. J56 plates might work since the JL8 rotor is only 3/8" larger per side. The plates would be a bit short of course.
Actually the plates only shield from water and mud spray. They aren't really needed for us fair weather drivers. Even in the rain it's not a problem. Driving on muddy roads without shields would cause rotor and pad wear.