Ok,I know the truck you are talking about,it has been on Ebay twice and it's in the classifieds here,and has been for a while.
It is a Mack powered M54A1C with out winch,has the later smaller turbo if I remember correctly from the pics.
The owner states it runs great and needs brake work,has been stored inside I believe.It has the earlier Ross Hydrapower steering.
The Good,
The Mack is a powerhouse in stock form,and will stand a little tweaking powerwise,I would say at least 250 hp with the proper modifications.
The truck looks to be in excellent shape in the pics,If I didn't already have 10 myself,I would have jumped on it,if it wasn't so far away.
The 5 tons have better brakes and good hyd power steering compared to the deuces,again,in my opinion.
It's a dropside truck,rare in the M39 series trucks,if you are planning to modify,bob or turn it into a major off road truck,probably not the best to start with,just my opinion.
The BAD,
Mack parts are EXPENSIVE!!(I know,I have 4 of them) expect big repair bills IF it develops engine problems,especially if you cannot do the repairs yourself.
The ENDT series Macks have a flat tappet style camshaft,they are succeptiable to lobe wear caused by the lack of zinc in modern diesel oils, a AFTERMARKET(not Mack) cam kit will run you about $2000 ea when(not if) it needs to be replaced.
If this is your first MV purchase,I would recommend you go for a deuce if you want a big truck, 5 ton parts are about double the weight of deuce stuff,and usually more expensive because of the commercial value of these trucks.
If you are thinking that you can run WMO,WVO or anything but 100% pump diesel in the Mack powered trucks,you can,but they absoutely HATE IT,PERIOD.
The APE series Bosch injection pumps weren't designed to deal with fuels that viscous,it cuts the power almost in HALF, speaking of injection pumps,IF you run WMO or the like through it and wear it out prematurely,it's an $1800 rebuild on the IP itself,not counting $150 ea(x6) for the injectors.
The Mack is only gonna get about 5 to 7mpg on diesel fuel,that's keeping it at about 2000 rpm/52 mph.
Once again,this is my opinion on the subject,based on facts I have learned about the Mack powered trucks after having owned several.