Improving stride length

Uphills to increase stride length, downhills to increase run cadence.

Plyometrics and hip extension exercises.

Speedwork

For me I used to run 3:00/kms at around 198 cadence.

Then started doing a lot of treadmill work, did most of my sessions over this winter on the treadmill. I think by default you run much more efficiently on the treadmill at fast paces, so within a few months my stride slowly adapted. My cadence on the treadmill was much lower than outside, but it translated to a slightly lower outside cadence and a more powerful stride.

Now I'm around 190 cadence for 3:00/kms, but stride is much more flowing and efficient.
I'm not sure if it will work for you, but it did for me.

Hill reps. Not just running a hilly course, but weekly sessions of long hill reps. I'd suggest 10x45 to 90 seconds. You could do 45 seconds one week and 90 seconds the next week. This will strengthen your legs to lift your knees, which will translate to a longer stride on level ground.

This doesn't have to be a separate workout. When I was distance training, I would run 3 miles to the hill, do 8 to 10 hard uphills of 45 seconds with walk down recovery. Then, I'd run three miles back. That would give me 7-8 miles total for the workout.

I strongly suggest that you jog or walk the downhills. Save your energy for the uphill reps. The downhill is recovery. The risk of injury on fast downhills is much higher and your cadence is already fast enough. I lost 6 months of training to osteitis pubis (pelvic bone) from fast downhills. It can be a career ending injury.