The latest manual should be Mercruiser Service Manual 31 Merc part number
90-864260T00 which covers the newer engine models 5.0L (305), 5.7L (350), and 6.2L (377).... 90-864260T00 Superseded from the older manual # 31, Merc part # 90-864260001 and shows to cover right around the 0M300000 + serial number ranges which also shows 1A***** + serial numbers. Search 90-864260T00 online and EBay.
There's also a supplement manual that seems to cover the EC exhaust system and a few other components at affordable prices you may want to consider getting as well on top of the latest service manual 31 90-864260T00...Merc part number 879288023,
http://www.ebay.com/sch/i.html?_fro...1313.TR0.TRC0.H0.TRS0&_nkw=879288023&_sacat=0
Bear in mind though, should you be looking for a wiring diagram for the newer engines, the detailed wiring info won't be found in the service manuals any longer as that type of info is now found elsewhere for the dealers after 2007 and may require either a merc dealer or possibly try Contacting MerCruiser Customer Assistance to help find the correct "Wiring Binder" part numbers for your engine.
https://www.mercurymarine.com/en/br/contact/mercruiser-customer-assistance