Accually whoever said 351M sucks gas? refering to the engine sucking or its gas sucking abilities? Really its a pretty efficient engine - it breaths better than a windsor thanks to its Clevland heritage, although it is a 79 so that might hurt you some - with the emmision stuff. But I have a '78 with 36s that'll pass emmisions and it gets 13.5mpg. Most people stick a massive carb on there looking for more power - These are trucks people CFM helps at 4-5K how often do you rev you're truck like that. 450CFM would probably do it for most people - just as much torque better throttle response and mileage. But the motor does kind of suck - except for the Big block bellhousing bolt pattern. It has a pretty bad oiling setup (It oils lifters first, Mains and rods tend to get starved in old loose motors) but it can be pretty well shored up by taking a oil line from the rear of the motor, the galley that they stick the pressure sensor on, up to the front by the filter where a sending unit would go on a Windsor. Otherwise the motor is built like a brute. But you may want to consider a 390 or somthing it'll bolt up to you're transmission as well, 460 might be a little over the top esspecially if you want to use it for trail use. The truck sounds well equiped if the work is done well it could be worth 5500, If you really need somthing like that - or you could get a pretty stout preformer set up for alot less if you do it you're self. my 2 cents.
'78 Custom 4"Lift 36"HummV tires Factory Rollbar-QuadShock-4Speed. '78XLT A/C, Cruise. '83Custom A/C and sweet paintjob.