Hey Willy,
I like the later model V20's because they have a full liner inside. Check the gallery. I don't know to much about the OMC outdrive systems, I'm a Volvo/Penta guy.
Here is a couple of links that can answer the FWC conversion kits and benefits. I haven't decided if I'm gonna add it, my original engine lasted 20 years and the manifolds and risers lasted 17 years - with good care.
http://i-netmarine.com/fwc/questions_fwc.htm
http://i-netmarine.com/fwc/Volvo_Pen..._All_Years.htm
http://www.monitorpro.com/shell_and_..._exchanger.htm
I'm not 100% positive, but I think some of the older hulls have a 20" transom ( outboards ) I would want a 25" transom for sure!!!