Most carbs work best when they're level but there is still some leeway and depending on how the truck is loaded or not it may or may not have the carb surface on the manifold dead level when the truck is on level ground.
I like the original question if you're trying to put it back together as originally designed then reference the angle between top of the block (or oil pan rail and/or similar parallel surfaces) to the straight part of the frame rail.
Grigg
