If the photo is common to all you riding (looks nice), you could get away with a rigid (which can be better than a budget fork).

For the headset, not sure what you mean by oversized, 1 inch was standard till about 1993/4, when 1 1/8 inch took over, Evolution or 1 1/4 briefly appeared on some bikes.

For the price difference, would probably go with the du Mont, as the difference should cover cables, cassette, chain & possibly chainrrings.