Oh. My. God. Alex, your Harrison is truly a stunning piece of work! Well executed, in every possible way. Wow. The Stronglight 57 crankset is just marvelous. Congratulations! Thanks for the flickr set, it's fun being walked through the restoration and build from its initial stages..
I agree, the gearing might not be adequate for hill climbing, but at least you've kept it true to its racer origins. For regular riding, you could always throw a Stonglight 63 on there, for which, despite not being period correct, at least finding smaller inner rings should be fairly easy. Then keep the 57 carefully packed away. Looks like the Simplex front mech can handle a much smaller inner ring.