Primer or filler to sharpen body line

I’m working on a 87 Camaro and want to sharpen the side body line. The current body line is rounded and l’d like to make it have more of a crisp edge. I originally thought I’d use Slicksand and sand up to a taped edge from the top then the bottom to sharpen that line. But now I’m thinking it might be easier to maintain a straight line if I stack 3 or 4 layers tape at the body line then apply filler up to the tape edge, remove the tape then apply filler where the tape was. Any suggestions on if the primer method is better, worse or no different then using filler?

This yellow line is the side body line I’m talking about.

Why you would want to do this notwithstanding, the better way to sharpen the line would be with slicksand and blocking. If you are worried about maintaining a straight line then using filler will be much more difficult to maintain the line especially if you don't have much experience.
Use a guide coat and crosshatch the top after applying slicksand. Use the line at the edge of the fender and 1/4 for reference and as a guide.
Block (crosshatch) some on the top(above the line). Reapply guide coat and block the bottom (below the line). Never sand over the peak (line) just sand in that plane whether on top or bottom. As you do this you will start to see the line become more defined. Allternate top and bottom keeping your eye on the line and the edges of the fender and quarter. Do what the line tells you. If it's low sand more on the bottom, if it's higher in places then sand on the top Keep re-applying guide coat. If you get stuck or lost run a line of tape from the fender line to the quarter line and guide coat over it. Pulll the tape and you will see where the line is supposed to be.

Easier to show you all this than try to describe it. So ask questions if you have them.

As always Chris has given great info. Funny the 96 Bronco i am restoring my customer wanted to soften the body lines up a little.

It would be very vulnerable to chipping.

If you never sand over the body lines when blocking you will find your body lines sharpen as you go. I usually have to blunt them a little when I’m done. Paint doesn’t like to stick to sharp edges in my experience.

Some folks view sharp body lines as a sign of quality work. C2 Corvettes often get almost razor sharp body lines when done by high end shops.

Don

Thanks Chris for detailed reply, great info. As to why, this car has a nose from an 84 which has much crispier lines to it compared to later years bumpers on 3rd Camaros. I think it would be a fun little detail to have the side lines be a closer match to the nose. I’m not wanting a razor sharp peak, it would be softened but with a tighter radius compared to the factory radius.
This is a father-son project car so it if looks bad or we start getting concerned about excessive build to get the look we wanted we can nix the plan.

I wanted to give an update plus thank everyone again for the advice.

With all the doors and fenders on the car, I aligned the panels and taped a string along the body line and made marks on the inners edges of the fenders, doors and quarters along the string line. Then I could apply my tape line using either the string line or those reference marks to keep it perfectly straight.

I’m very pleased with how it came out and wasn’t as much work as I thought it would be.

Good job David!

That came out really nice. I've made notes on this thread. This is the result I want.