What year backing plate assembly do we need ?
Also are you using the stock 914 caliper or do you switch to the 911 ?

I have a set of hat's if you go with 911 SC stuff. I will not be able to use them on my build.

You need a specific 911 wheel backing plate and bearing cover - I wanna say mid 70s will work, but I will have to look. I have quite a lot of photos of the process but have not yet posted them. I went the route of installing the thick metal stop and using VW bus cables in extended 914 tubes.

Before you say it, I know or at least my contribution

Oh I forgot 911S aluminum in front and 911 M calipers in the rear. The latter are easy to come by. For calipers PMB is always a good deal.

PMB makes aftermarket 914-6 calipers. It's a lot less hassle than the 911 ebrake.
http://www.pmbperformance.com/914brake.html
Here's alink to a how to article on the 911 ebrake conversion.
http://www.914world.com/bbs2/index.php?showtopic=4909

I am running the 911 ebrake with boxster rear calipers. I had a member here weld the stop plate to my trailing arms. I am not a fan of the stop plate on the backing plate. It's not as strong as how the factory did it.