How much oil is being pushed out of the engine through the crankcase vent? If the valves have insufficient lash or the rings/cylinders are significantly worn oil consumption will go through the roof with the oil being blown out with the normal blowby gasses. I do think that you can burn a quart of oil per 450 miles without seeing smoke in your car. If your crankcase vent is circulating to the air cleaner remove it, tape the hole in the aircleaner with duct tape to prevent unfiltered air from entering the engine and let the vent blow onto the fender well. After a drive long enough to get the engine completely warm with some high RPM operation check the amount of oil on the fenderwell. You will see some oil, and that is perfectly normal, but if you get a significant amount you will know where the oil is going.

I am not sure on the 240, but the 300 engine valves are easily adjusted without the special or bent wrenches. It does help quite a bit to have one for the lower nut ground down to about .2" thick. Hope this helps.