Dunno if they were an option but my 84 944 definatley has what apear to be, built in anchorage points (the car did have rear belts but they were binned along with the rear seats).
The 928 S2 had lap belts, but that changed to 3-point ones with the introduction of the 928 S4 in 1987. You can also fit a child-seat in a 928. Porsche still sells them... Buy a 928 over the 944 anyday! Not that I am biased