Just looked at the serial number and some quick research on the net- several sources seem to agree- the first two numbers on Atalas are the year of manufacture-

this one is # 75 D 1045

1975 I presume- I would have guessed two or three years older-
and with original simplex shifters- a small "Simplex" sticker still on the frame- a bit unusual for an Italian bike to be fitted with french stuff- wonder what the original brakes were- I have the front center pull hanger in my hand- probably the original:
fairly rusted and don't see markings- don't recognize it offhand- don't think it's Mafac though- has a QR cam adjuster
maybe I see some etching that may be revealed with some WD-40

besides the simplex derailleurs and shift lever, Ben sent me the headset, "pivo" style TTT vintage alloy stem,
and steel cottered crank- fairly rusty- don't think it'll go back on the bike- never liked cotters much and very heavy- Nice museum piece though-
I'll probably PAINT IT UP! Chrome paint, sell it for new.....

Probably set it up with this crank-

1975- Moody Blues split up and two members put out this album The Blue Jays. My Little 500 bike team was traumatized by only finishing second in our first year without Olympian and National Champion Wayne Stetina- in the 25 running of the Little 500- up to 60-something this year I guess.