The later engine the better. The crankshaft was upgraded in the 1988 model year, and the connecting rods in the 1989 model year. I would buy a 1990, or later, engine.

There are a few specific details to attend to at engine swap time with a newer engine. I'll cover them know, but re-post when you do the swap. For a 1990 and later engine (they use a different fuel injection system), you'll want to use the original distributor, throttle body, Idle Air Controller, and engine wiring harness. The newer injectors are a little different, and I've run both, but I see no reason not to use the new injectors. The O2 sensor will make up for the very slight difference in rated flow.

The 1987 and later B230FTs have a much improved oil filter mounting. You'll want to leave that on the engine. Use the newer turbo, if the engine comes with it.

The Coolant Temperature Sensor (under intake port 3) is different on the later engines, but it works fine on the early engines, but not vice-versa. The Sending Unit (under intake port 2) for engine temperature is single wire. You'll want to use it in the later head.
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john