Re: V-8 in a 185?
I don't think it would that big a deal. Bayliner has made several boats in that size with 5.0 and 5.7 litres motors. Not that much of a stretch.
However, regardless of that fact I would take the time (once the existing motor is out) to get some marine/pressure treated wood (plywood or whatever) and add some bracing into the bottom area around the motor mounts. I would both fasten and fibreglas them into place. This would take a few hours and is not that difficult and would/could prove very useful in stiffening and stabilizing the back end of the boat.
Good luck.