Absolutely keep the 283. A great engine. Plenty of parts and power. Especially if it's a "numbers matching" engine. Meaning that it's either THE original or the serial/casting numbers are 1966. If you decide to go 350, the 283 is valuable to the right person. So don't junk it. A 350 will not give enough more power to make it worth ruining an otherwise stock truck. If you were going BBC with all kinds of mods to the truck, then bye bye 283. Also a 350 after 1972 will be a much lower horse power due to Gov't required smog control legislation and could be a real gas hog. In the end it's your call, you sound like you already know the story.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn