CB550 fiberglass seat

I just got a 73' CB550. I really want to make a cafe-style bike, but I am having some trouble finding parts. I really want a fiberglass cafe seat but I can find are seats made for 400s and 750s. Are either of these interchangable with a 550 seat? If not, do you guys know which would be a closer fit? (I am a beginner, this is my first bike so I would like the parts to not require a lot of modification).