The OAI intakes on all 455s from 1970 to 1972 have a pressed in fitting in the intake for the PCV. The hole for the fitting is open to the lifter galley. The fitting is approxiamately 1" to 1 ¼" high, and sticks up about 7/8".
On non OAI cars this same arrangement was used on four speed cars with iron intakes, while automatics had the PCV in the left valve covers. The fitting is also used on aluminum W car intakes. 4 speeds used this arrangement because the air cleaner was dual snorkle, and so the PCV went from the intake to carb.
A 90° rubber nipple goes between the fitting on the intake and the PCV valve. A short hose goes between the PCV valve and the base of the carb. This set up allows the use of two breather tubes between the air filter and the valve covers for better crank case breathing.
The GM part number is 405143 (description NIPPLE, ventilation (steel-1 ¼"). In addition, this was used (according to my parts illustration book) on many applications including, but not limited to, '69 H/O's, '70-71 OAI w/AT or ST, & all '72's with OAI and or ST, 73 A-Bodys w/ST, and 73 A-Bodys w/L77 and M40 AT.
[ Thanks to Dave Wyatt, Mark Prince, Kevin Hoopingarner for this information ]