Yea,definitely find out if it has the lucas brake system!They can be very problematic and expensive to fix.In fact most of the time it's cheaper to put in a different rear end with a different brake system,than it is to fix the lucas stuff.I know this from personal experience.When the lucas system works it's a good system,but when it doesn't,be ready to get out the check book.I'm not sure if the f600 was available with a 5.9 cummins,i have an f800 with the 5.9 I've had good luck with it it's a well understood engine at this point because it's been around quite a while.If it's a gas,I think all of ford's industrial gas engines are fairly bulletproof.That's my 2 cents