you sure about the vtec cronic? i never heard about a vtec-zc, and i thought i knew everything about zc's. anyway, here is the TRUE answers to all your zc questions for the under educated.

D16A8 ~ European model - fuel injected without catalytic converter
D16A9 ~ European model - fuel injector with catalytic converter

ZC ~ Japanese model - comes in several varieties. Injected, carbed, sohc, dohc, brown valve cover, obd0 and obd1.

For the 88-91 CRX/Covoc you want a ZC with a black valve cover with the cover bolts on the sides and the Honda symbol on the exhaust side of the valve cover. They come with a 4-2-1 style exhaust header and a small oil to water oil cooler on the back of the block. The engine mounts are the same as the 88-91 Civic/CRX.

Note - be sure it has a black valve cover with the cover bolts on the front and back edges of the valve cover and that it is a DOHC design. There is an older ZC with a brown valve cover that you don't want! Also watch out for the Integra motors which look identicle to the ZC except for the valve cover bolts are not on the edges of the cover, this motor will not bolt into the car.