The Z24i had throttle body fuel-injection. The Z24S was carbureted. The only version used in the D21 Hardbody in the US was the Z24i and it was only used a couple of years before being replaced by the KA24E engine. The Nissan Z-series engines, sometimes called "NAPS-Z," were hemi-head engines and, if my memory is correct, used the engine block from the ol' L-series 4-cyl. that appeared in a number of Datsuns, like the 510, 610, 710 cars and 620 truck. While NAPS-Z engines aren't talked about much these days, they were a pretty innovative engine in their day---Popular Mechanics Magazine even did an article on it---due to their ability to recirculate a large amount of exhaust gas ("NAPS" stands for Nissan Anti-Pollution System). It came in 2.0, 2.2 and 2.4-liter displacements, some with 4-spark plugs and most with 8-spark plugs. Some had single-row timing chains and others had double-row timing chains. So, not all NAP-Z engines are the same. There are probably a number of parts on the '81 engine that would interchange with yours, but I don't think I would pay $350 for spare parts engine. Not unless you are considering swapping your throttle body injection for a carb setup, but that would be a mistake in my opinion. The "Electro-injection" throttle-body Z24i is a pretty stout engine! Yeah, it's not big on horsepower, but it does a pretty good job of getting a Hardbody truck around. You don't run into many timing chain issues with them, although you may run into a failed head gasket once in its lifetime or an occasional failed throttle body gasket or intake manifold gasket. There's a whole bunch of vacuum hoses, as you found out, but that was par for the day; they were nothing compared to the vacuum hose mess that Honda used on old Accords! Avoid aftermarket ignition parts water pumps and do basic maintenance and they tend to last a long time!
