the reason some people dont swap intake manifolds now is because the sensors that are required will still work, but i know the design of some of the plugs (coolant temp sensor comes to mind, maybe one of the iacv ones too) are different, s13 coolant temp uses plug with that stupid wire clamp thing (looks like an injector clip or z32 mafs style clip) where as s14 uses a tab depressed connector. ive never kept manifolds, i just found it easier to swap them, and take care of welding things shut while they're out.

i've never heard of the s13 having a single row upper timing chain though. even sohc's have double row.

and all s13's had the 240/248 camshaft combination except 1994 models and late late 1993 models when they used the new batch of motors with the 232/232 cams and the scv were ditched as well.