The focus seats has been done before so I know they fit. But not sure what us involved.
I've not heard of a 1.7 in a mk6 fiesta, but it not a bigger angine than the 2.0 duratec found in the st. So should fit in there not sure on what mounts you would need to run it on and what ecu you would need first thought would be aftermarket but could be wrong.
Running the 1.7 staying na ford had a racing puma which was 155 so you should be able to get close to that but the inlets for the racing pumas are like rocking horse poo so expect to pay a lot for one. Throttle bodies are do able but would be on par with a 1.6 and more hassle as the 1.7 has varable cam timing.
But so get near the st power you would need. Full exhaust manifold back, cams, air filter and a map the inlet would be up to you if you wanted to pay the price for one.