While your idea to preserve the simplex front is commendable for originality, I'd recommend replacing it with an alloy FD...I've had a number of delrin simplex front derailleurs and every one has had a crack somewhere.
I had had my share of broken front
Simplex derailleurs, the Delrin plastic is light but not durable. None the less, I am a bit of a purist and still have a several stashed in a box.