Dave,
Your idea is the way age-group athlete trained for years. It’s not a terrible way to train. It increases specificity at the expense of run fitness. Your proposal will work, we just think that our method is better.
There are just 4 mid-week long run sessions in your plan: weeks 16, 17, 19, and 20. If you can pull of 1 of those mid-week as scheduled, great! Two? Fantastic. Zero? No problem.
Another option is to switch up the long ride and run: Do the long run Sat and long ride Sun. I’d just do this once.
Maybe an ideal compromise is one mid-week session that you manage to pull off, one run-then-bike Sat-Sun “brick” and two bike-then-run Sat-Sun bricks. Gives you two long runs on fresh legs.
David