Yeah I checked.  The Yamaha bolt pattern looks standard, but the Merc looks like it might be the older pattern...I heard there was a period from late 70's to sometime in the 80's that the bolt pattern was different.  Maybe the lower unit is older than I was told? 
  
The bolt patterns look like this (roughly): 
o = yamaha 
o = merc 
  
oo-------oo 
  
  
-o-------o- 
-o-------o- 
  
Thanks, 
  
David
		 
		
		
		
		
		
		
		
		
	
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