The Ecam is designed to be used with better flowing heads, intake, exhaust, maf, as well as a steeper rear gear. I think you'd be much happier using the 1.7's and the stock cam with the Cobra intake rather than the E cam. However, if your valve springs are tired, the 1.7's will make them more tired more quickly. They increase peak lift from .444" to .472" which makes the springs work harder. As for power increases - I've seen dyno tests that vary all the way from a gain of 18HP to a loss of 1HP for 1.7's being added to engines. It's virtually impossible to predict how much or if they'll help you. Your money is much better spent on the intake manifold - it is the biggest bottle neck to flow on the stock engine, and it (Cobra or have your stock lower ported by tmoss) along with a decent exhaust system and steeper rear gear will make a noticeable difference in the car's performance.
You'll be hard pressed to find someone that has bothered to spend the money to do a before and after dyno with just the intake change. However - send a pm to tmoss here on the site. He is very experienced with the stock Ford manifolds (stock HO, Explorer, Cobra and GT40) and can give you a good idea of what to expect from the intake improvement.
I'm getting a set of 1.7 rockers for free. Wondering what is a good cam with a good amount of lope to use with these rockers? The engine is a 79 302 rebuilt with 40k on the engine. Also have a Holley carb and performer intake.
Also might be selling them if anybody is interested.