Here’s the skinny
The comments about the J block are correct, but it wasn’t always used. In the block sequence numbers where Buick would have explained everything is a smaller upside down alpha-numeric code, most start with HI the jetfire block starts with J.
The valve covers do have the oil return bung on the passenger side. The oil cap is also relocated forward, as standard olds it’s located in the middle and that where the downpipe and exhaust turbine chill, as well on the driver side where the carburetor and rocket fluid metering equipment is. Pretty much gonna find em on a motor or nowhere.
It’s like the flex plate on a 61-62 tempest. Only gonna find it on a motor still in a tempest. If you pulled it for whatever reason you would find out really fast when you somehow ignored how shallow the bellhousing is. These are engine and Car specific parts. Plus to make it worse Pontiac offered a recall to convert you to 4bbl. Also the drivers side exhaust manifold is special, it has a different angle on the choke heat provision, as well as for the crossover pipe to connect both manifolds.