It's been done. I've done it. You may need to trim the two mounting pegs in the frame to get the tank to slide on but it will work. The other issue is length. The seat needs to be trimmed or moved back slightly for the bigger tank to fit. Looks wise, I like a big tank so I think it's cool. I had a 750k tank on my old '76 550 with a slightly smaller stepped aftermarket seat and it just fit. I recently helped a friend put a 750F seat on his 550 and it was quite a bit too long. We had to change the brackets on his aftermarket cafe solo seat to get it to work. Awesome when done, though.