+1 I have seen hundreds of these and the only absolute is there are always enough ports. Regarding the rear fittings, I think the second picture with the nipple coming out of the top of the larger rear fitting is a later detail, like around intro of CJ engine 4/68 ish. The rear small block can be 1-3 nipples and I've seen as many as 2 capped. I agree with others motor goes to front steel fitting
The fittings I photographed (not the WCCC photo) came from an engine with a 7M build date. All of the castings were 7L, the distributor was 7L or 7M, and it did not appear that the PCV system had been taken apart prior to my acquiring the motor. So the fitting with the top port may have been used a bit earlier. One factor may be what vehicle the engine was in. I don't know if it came out of a Fairlane, Cougar or Mustang. It's a 322 code (M/T) engine and the distributor was a C8OF-C, so it was an S code motor. For a 2/68 SJ Mustang with A/T, do you think the fitting without the top port (shown below) would be more appropriate?