Do you mean as a parallel twin, or V twin?

have at it...
http://www.musketvtwin.com/

Or like a double engine dragster?

It would be a lot less work to convert a 1400 Intruder to belt or chain drive and you would have essentially the same thing as two Savage engines together anyway.

But you could do some interesting things with the two Savage engines idea. Run individual cranks gear driven from each other. One crank would rotate backwards from the other then. If the two are phased correctly, vibration from one would be cancelled by the other.

No I haven't but to be honest I first saw this motor, the three cylinder, in a Wooden boat Mag. it was used it the Farnsworth trophy race ,an international boat race held on the great lakes back in the 1920 -1930s The year it ran it won the trophy ! The races where around a course in the lake 3 races in 3 days . Most of the boats were large 25-35 ft. and carried between two and four inboard motors and turned in brake neck speeds (for the day) of about 60 mph. This motor was very small and produced only about 25hp but was in a boat 22ft. long but only about 4 ft. wide ,it cut through the water at about 25mph. the winner of the race was determined by dividing lap times by cubic displacement so it won ! and made a lot of big boat owners very angry.