I spotted this and although I'm far from an expert on the 70 model I can give a brief on the models and if anyone has any specific questions they can email and I'll give it a stab.
They were first introduced in 1960 as a successor to the model 1935 the roman numerals on the trigger guard indicate date of manufacture but are actually numbered from 1954 starting with an X therefore XXI would be 1965. The date codes change at XXX 1974 and go to the alphabet AA 1975, AB 1976, AC1977, AD 1978, AE 1979, AF 1980, AH 1981.
The first model 70 was in 7.65 with the sights, front and rear, fixed on the frame.
The first 22 was the model 70s with the front sight on the barrel and an adjustable rear sight on the frame and 90mm barrel steel frame or alloy frame, I have steel frame.
The 71 had fixed sights front on barrel and rear on frame with a 90mm barrel, mostly alloy frames.
The 72 is the same with the exception there was a 150mm and a 90mm barrel mostly alloy frames usually came as a kit.
The 73 has both sights mounted on a 150mm barrel, unusual configuration with the rear sight on the barrel, used a lot for target, mostly alloy frames.
The 74 has a 150mm barrel with adjustable rear sights, mostly alloy frames.
The 75 has a 150mm barrel with fixed front and rear sights, mostly alloy frames
There are other small iterations of the models but this is probably more than you wanted to know. The 70s is also made in .380 but I don't care for that particular caliber in that pistol even though it is the most plentiful.