I have no personal experience with the GM 6.2/6.5 other than riding around in HMMVs, but I think that a lot of people give these engines a bad rap.
Of course there are known issues. There are known issues with Toyota engines (1FZE head gaskets(small %), 3.slow, etc.) and all manufacturers as well. I wouldn't let that dissuade you.
Some people simple dislike them purely because they are a GM product. I personally have never owned a GM product, exception of my GM owned Saab. So, I don't really have an opinion either way.
Of course I would love to have a Toyota diesel in my 55. But, for some people, depending on what state they live in with regard to smog laws, parts availibility or mechanical ability, having a Toyota diesel is just not an option.
I can personally think of at least 3 people who have swapped the GM Diesel engines into there cruiser and have been happy with them.
I say go for it if thats what you really want to do. That's just my $.02...
Here's a couple links of non-Cruiser related swaps.
http://www.dieselpowermag.com/tech/chevy/0554dp_62l_buildup/index.html
http://www.dieselpowermag.com/features/trucks/0704dp_1978_international_biodiesel_scout/index1.html