I seams I cant post the link to the chinese Diesel outboards. My solar business has used www.Alibaba.com
in the past as a resource for parts etc. I just happened to have a few minutes and typed in Diesel outboards in the search page and up they came. I know that Yanmar stopped building their wonderful outboard motors a few years ago but you can even find a few of those on there too. What i found were between 4-10 HP. With the reputation of diesels for high torque at low rpm I was thinking the 10HP might be a good engine. They are air cooled it seams which may make them noisy (I dont know this) but the weight seams acceptable. There are also low cost,light weight very compact diesel water cooled engines of low HP that would be ideal for a hydraulic set up or to put to a high output 12 volt alternator. The site is partly owned by Yahoo and i have not had any bogus problems with it but like all sites there are always the bad guys lurking so make sure you have antivirus switched on.