The '69-'70 deck height is 9.480" while the '71-'94 is 9.503". I looked at MSD's 351W distributors listings and haven't found a separate part number for the '69-'70 so hopefully that means Ford didn't change the distributor dimensions.
From the Ford Motor Sports book:
M-6605-A341 HD oil pump drive shaft for 351W.
NOTE: Will not fit EEC-IV equipped engines.
From this information, one would guess that the electronic/computerized distributors are different if the drive shaft will not fit. IIRC, the 5.0 EEC-IV distributors are longer/shorter??? than the old points/Duraspark distributors. So, maybe the later 351W distributors are different than the older points/Duraspark ones also. Of course, the blocks themselves make no difference in the distributors, just that the associated distributor parts be compatible.