I have almost the identical bike. I think yours is a 1973, my bike is a 1971, and has a headbadge, not a sticker.
Mine still has the Leotard pedals and Mafac brakes, but, a bunch of the other stuff has been replaced. Alloy wheels, Suntour AR derailleurs (the Simplex were sunburned!) and some other alloy bits. You can improve the Simplex shifters, dramatically, by taking them apart, scuffing and cleaning the metal outer cover and the plastic shifter handle, and epoxying them together. Much improved stiffness, and nobody knows it has been done.
I have a Gyes Brooks saddle copy on my bike, mine was pieced together, and I think most of the parts I replaced were pretty low end entry level bike stuff, the bike is a joy to ride now. I had a bent fork that caused me huge issues, as it was bent up on one side of the brake hole drilling, weirdest thing I have ever seen, and a bugger to diagnose. About 3/16ths difference between the length of the legs, and it made it miserable to ride. A Tange fork and headset off a Schwinn Traveler bolted right on, and I never looked back.
Haven’t rode it in a while, should have thrown it away, in hindsight, but, some bikes just get rescued.
Ted