Need to identify the year of this 200 outboard, 20 hp

[Force 120]

Hello,
Please help me to identify this 200 mercury outboard. There is no serial name plate anywhere on it.
I attach some pictures of it. The compression is 110/115 psi and has strong blue spark but I could not remove the lower unit out of it to change the impeller. Two nuts have been removed.

 

[racerone]

Those decals were used in 1976 and 1977.------There is ( hidden ) a third nut / bolt.----Find it and the lower unit likely will fall off.

 

[Force 120]

Those decals were used in 1976 and 1977.------There is ( hidden ) a third nut / bolt.----Find it and the lower unit

 

[Force 120]

There are two nuts have been removed and the third bolt on the top but I could not get any Allen key to fit on. Any suggestions to get this bolt out ?

 

[GA_Boater]

I think the allen bolt is 3/8". All my Mercs are that size.

A serial number is more important than the year of a Merc. What serial number is on the plate between the transom clamps?

 

[racerone]

There is a bolt hidden under that trim tab.------You have to get this tab off.-----Or bring it to a shop!

 

[Force 120]

Finally locate the third bolt which holds the trim tab. This is 5/16" socket head cap screw. Then there is a third nut behind the trim tab. After removed it, the lower unit came apart. Note: could not find the serial number anywhere on the motor.

 

[GA_Boater]

Finally locate the third bolt which holds the trim tab. This is 5/16" socket head cap screw. Then there is a third nut behind the trim tab. After removed it, the lower unit came apart. Note: could not find the serial number anywhere on the motor.

It's on that plate.