Re: '57 FD-11 hood on '55 QD-16
That's a nice motor. I've got one, too. Place a free ad on aomci.org's free ad section and someone will be kind enough to fix you up for a good price. THat's a one year only cowl. Evinrude cowls won't fit a johnson. Another QD cowl might fit from '55 to about '58, but would be the wrong color. You might also try laingsoutboards if you're in a hurry and don't mind price. I've seen 'em on ebay before, as well. There are a couple of guys that sell lots of old OMC parts you might ask on ebay as well----they're pretty high.
Good luck,
JBJ