The terms "70 series" and "80 series" apply to Colts and indicate whether the pistol has (80) or does not have (70) the firing pin block. I don't know if the PT1911 has a similar block or not, but if they do they either have it in all their 1911 type pistols or they have a different way of indicating it.
The best way is to order the part and give the gun's serial number; that way the factory or the parts supplier can get the right part to you.
Jim