Could be, without the engine number its hard to say but its the right "sort" of engine for that bike...
With any collectors' classic bike (or car), it is always preferable to have matching numbers, i.e. the engine and the frame were originally assembled together by the manufacturer and are still together. In the case of Ducatis, the engine and frame numbers did not precisely correspond in the first place, because the factory put batches of engines in batches of frames more or less at random. If you had an engine plainly of the wrong type for that frame the value would be lower, and the bike would not really be a collectable. Since you have probably got a widecase 350 desmo engine in a widecase 350 desmo frame, you're doing pretty well. If you want to get really picky, and establish whether the engine and frame came from corresponding batches, you would have to note the frame number and engine number in full and do some research in reference books. Without the numbers (which you have not mentioned). there is no way to know.
