The badge on the side of the car said 4300
i just went through my information system. in 87 there was only the engines i listed....2.8, 4.1, and 5.0. the 4.1 was the good old ht4100, and to say it sucked balls is a mild understatement. the 4.1 was replaced in 1988 with the 4.5L. it too sucked balls, but not quite as badly as the 4.1. in 88 the only engines offered were the 2.8, 4.5, and 5.0. in 1991 the 4.5 was replaced by the 4.9. this engine was pretty good. there was also a 5.7 option added(this was the corvette engine).
if we go back to 86, there was a 2.0, 2.8, 4.1, and 5.0.
someone stuck a 4.3 badge on your car. there was never from what i can find, nor from what i have ever seen, a 4.3 in a cadillac.