If you're designing a new airplane, it's easy to do things like work out the least frontal area, or draw a good pressure cowl design.

When you're choosing what design structure, you're locked into what you think is at least strong enough structures. No wiggle room there.

If you're building a kit, there are often lots of places where you can choose to build parts of the plane with a different, lighter design. Or use lighter, stronger wood. Or add lightening holes. But little opportunity to change shapes or sizes. If you're assembling an ARF, ain't no wiggle room to do much of anything if you're like most ARF builders and pressed for time. On the other hand, awhile back, I chose not to use the horizontal tail from an ARF. The stab was made out of crap wood and the design was sticks. And the center section wasn't any larger than the fuselage so the LE was the only stiffener the stab had from it's TE forward. I laid out the same shape with a wider center piece, a LE doubler that went out about .3S, and added a couple of diagonals. Also used balsa that fit the task of each piece. After all, I wanted strength and no excess weight. Apples and oranges, but both good fruit. And the elevator was two solid pieces of some kind of wood that'd been good flooring. So that got flipped into the trash after tracking the outline. The new pieces were quarter grain, medium balsa. And since movable surfaces flutter relative to their mass, I used some hole bits and made a pretty row of holes along them. Looked sweet and holes are light, very light. Nah, it wasn't really an ARF. For sure it wasn't an ARFWVL. But it wound up as one. It didn't come out of the box Almost Ready to Fly Well and for Very Long. But it took to the air that way.

About the only place I can think of where weight and drag shows up together is wing fillets. You're doing a fillet to reduce drag. It adds weight. So you can choose to make it as small as possible to keep the weight down. And build it with as little weight as you know how. And you can control both. But it's easier to not do fillets at all.

So, are you looking for hints on where to cut holes in heavy ARFs? Or whether or not to throw out heavy ARF parts? If you're building a kit, you've got some room to do some things. Building a scale plane, only room to design in lightness. Almost no room with everything to reduce drag unless you're the designer. The word "reduce" suggests a starting point you don't control.

For the most part, you change shapes to reduce drag. The lesser part, you keep things smooth. Two different fruit.

Using lighter components won't change drag, except for induced drag that is. And components that don't change size or shape usually don't change the drag.

I apologize for not understand what you want to do. I would guess all this blather hasn't helped you at all.