My opinon???? not to often anyone asks Well just what are your plans for the truck and how are you going to use it? If its going to be a driver and you want to have some fun with it I would lean towards the Windsor. Lots of performance parts available to build it into whatever power range you want. Less weight in the nose so it will handle better than if you had all the weight of a big block up front. If built right you could still get halfway decent gas mileage (if you can even use that term on these trucks) outa her.
Dont get me wrong, I love the 385 series and even run one in my truck but for everyday use a windsor can be more than enough.
I guess i might as well keep the 390 and build it.Like Bore .30 put flat top piston.Shave the heads and put bigger valve in them.Put a good cam in it with a little hit to it.And headers and a bigger carb like a 750.Maybe more still thinking about what else.