V200 Blackmax model year identification

I recently purchased a Mako with what the seller said was a 1989 V200 Blackmax. The serial number tag that is supposed to be on the transom bracket is gone. I've checked all freeze plugs on the block. The only one with any info stamped on it is one on the top of the block that simply has "200" stamped on it. The only other identifying numbers I can find on the block are stamped on the aft end of the block, bottom right, just above where it bolts onto the lower unit. The numbers stamped there are 858 8631 C. That looks like the correct quantity of numbers/letters for the Merc serial number but I can't find it on any online reference. It certainly doesn't match up with any 1989 serial numbers. I had to replace the exhaust manifold cover. The exhaust manifold cover on the engine was NOT the one for a 1989 motor but was the one on 1988 and earlier motors. The carbs are WH models. That's about all i can tell you. Anyone have any insight on how to determine exactly what model V200 I have? Thank you.