Glad you asked:
Both trucks were rode hard. Typical wear items: Brakes, ball joints/tie rods, shocks, steering boxes, PS hoses, brake lines, cooling lines and hoses, radiators, tires fuel pumps, tanks, etc. The F450 has a new clutch and transmission housing (known to crack). Both trucks had significant rust (not uncommon here) so sand-blasting, painting and body replacement. The dump body, subframe, hoist and installation on the F450 was about $12K. Just put a poly fuel tank in the F450 (this past weekend) so that was another $1000 with straps and associated parts. The K3500 will eventually get a flatbed.
Specific to the dump itself, the bodies are prone to rust because they are usually made of mild steel, have poor paint jobs and don't get washed to often. Should be a lot better in WV. The hoists can give some trouble, but simple electric over hydraulic pump systems are not to bad to replace. Same with PTO set-ups. Look for a power up and power down hoist. Its a minor detail, but makes a difference when a gravity hoist gets stuck (I've had that happen). Make sure to prop the body properly if working on it raised.
The diesels add more complexity and cost, but really its the old part. A dump truck rarely becomes a cherished classic that leads and easy life. Most are driven by people who don't care about the truck. When they are worn out, they are sold off.