There's nothing scary about a belt as long as you make sure you change it on time, and do the job right when you do it. I would bet there are many, many more instances of timing *chains* breaking on old school pushrod V8s than there are of timing belts breaking within their rated service interval. If you let one go too long, well, yes, it will break... but change it on time and it will never give you any trouble. Changing them is not a hard job if you have the tools, and they make the engines quieter and smoother and more efficient than an equivalent chain-driven motor. A good running D24T with a stock exhaust can be amazingly smooth, quiet, and refined, and that's partly because of that timing belt.
The big Navistars are great, I work on a lot of 6.9s, 7.3 IDIs and Powerstrokes. Even had to do the big EGR cooler upgrade on one of the infamous 6.0L Powerstrokes a few months ago... that was fun. The older Navistars are great motors, except for the coolant cavitation issue on the 7.3s... but as long as you keep your coolant in good condition they are great rigs. I like them better without turbos as well... if you have ever had to replace the rear two glow plugs on an IDI Navistar with a Banks kit on it, you will know why.
Volvo diesels are even easier to work on than the old Navistars. They are quite different but very nicely designed once you get to know your way around them. The turbos are much nicer to drive than the NA ones, though. Don't be scared of the turbo, it's all a very accessible setup and the stock turbos on D24Ts NEVER fail. I mean never. I have one with 280k on it that is still as tight as when it was new.
D24Ts are small diesels but they sound and feel big... listen to one with an open exhaust, it sounds like a little Cummins. When they are running well, they have lots of torque in the middle of the rev band and great flexibility. Driving my 760 feels a lot like driving a car with a small gas V8. Tons of midrange torque and good power right up to 5000 rpm.
