Well ..... This question got my curiosity up.
So ..... I took an Open Top and a Richards Type II apart to see what's what. Who's who, and I don't know .... Third base
The basic answer is yes. A Richards Type II barrel will mount to an Open Top frame. That is where it ends. When the Type II barrel is flush to the frame, there is a 3/16 inch barrel to cylinder gap. Would make for a pretty awesome fireball with a case full full of BP. But not so much fun to shoot. It would require a custom made cylinder. And still wouldn't look lake a true "long cylinder" conversion (see Long Johns Wolff's).
The actual long cylinder conversions utilized the 1860 BP barrel assembly, newly made cylinder and loading channel thru the recoil shield. Just like LJW's gun (LJW has some really nice toys
)
With enough money to throw at it, you could build a really strange looking "Frankengun" but I doubt you'd be happy with the result. Or the price (boat load of money).
Coffinmaker