I have a Merc manual from late 70's early 1980's that talks about their fuel hoses being rated for 10% ethanol. You might go through it and double check . . . Those excels are built on the 2.6L block . . . so I'm 99.9% sure any 2.6L lower will swap. They come in 1.86:1 or 2.0:1 ratios. SEI sells brand new lowers for yamaha 2.6L motors for $795 with a 3 year warranty.
http://www.sterndrive.cc/Merchant2/m...ory_Code=SE416
My budget prevents me from buying new outboards, but I have ZERO issue taking a well maintained older motor on a long ride. Those excels were strong for a smaller displacement motor . . . they have the horizontal front and make great power for a 390lb motor. Check the shift shaft when you have the lower unit off.