I don't see any real problems with the specs of these Volvos. They would work fine if the trucks are in satisfactory condition. I have looked at Volvos in all price ranges, I have never bought a high mileage truck. You generally get what you pay for.
I suspect these are all high mileage units. No warranty will be included or avaliable. If you have to spend 10K to get the truck in satisfactory condition, it will not increase the value of the Volvo, and you will still have a high mileage truck.
I have never bought a Volvo with a Volvo engine. In General, the market prices for Volvo engines are about 2K less than Cummins, Detroit or Cat. Any engine work required for Volvo engines beyond normal service must be done by Volvo dealers only.
You would not need to uprate the engine to 425 HP, but I think if you chose to do so, about $1,800 worth or hardware changes are required.
Have the seller send you pictures inside and out of the lowest mileage cleanest unit he has for sale. If it looks satisfactory to you, travel to the seller and inspect the unit thoroughly including tires, brakes, air systems, etc. Take at least a 50 mile test drive.
If I were you, I would then have all systems inspected by an independent mechanic. Have him make a list of any problems that might exist, and what each should cost to repair. Then you might want to have the engine dynoed, and an oil analysis performed.
If you buy buy one, conversion costs can vary from say a low of $2,000, to as much as you want to spend. Registration cost's depends on what the State you register in charges for fees and plates. Good luck.
Larry
http://onezman.tripod.com/onezmans.conversions