OP, if running 75mpw doesn’t compromise your ability to do all the other work at the level it needs to be done (including this CNS/speed development work that, yes, should be done during base phase), then it can be done. If you find that you’re not able to do the other work you need to do To develop as a runner at the effort level and with the form it should be done with and not get injured, well, then you can do it. Here’s how I would try to get there if I were you, and also build in an off-ramp for yourself before 75 mpw in case it’s too much:
-Race your TT
-Recover for a week, do one light workout, then race a shorter TT (either 3k or 1-mile)
-Take one week entirely off, then take another week where you run no more than 4 days, no more than 20 total miles and no runs longer than 6 miles
-Consider the next week to be week 1 of training, and build as follows:
Week 1: 6 days, 30 miles, no runs longer than 6 miles, 2 days of 4 x 100m @ 400m efforts w/ walk/jog back for recovery at the end of an easy run
Week 2-3: 7 days, build to 40 miles, no runs longer than 8 miles, build to 3 days of 8 x 100m @ 400m effort at the end of easy days in each week
Week 4: repeat week 1
Weeks 5-7: 7 days, build to 50 miles, and 4 days of 8 x 100m @ 400m effort at the end of easy days, add 1 day of 4-6 x 10s hills all out w/ 5 mins easy jogging recovery, build your long run to 10-11 miles and run it and up to one other easy run per week as a fast finish if you’re feeling good
Week 8: 6 runs, 35 miles, 8 mile “long” run, 3 days of 8 x 100m @ 400m effort
Week 9-11: Now your real training begins! Stay at 50-55 mpw with an 11-mile long run (can still be fast-finish For the final 3-4 mile if you’re feeling good), and add 1 day of 3 x mile (becoming 4 x mile, then 5 x mile) w/ 90s recovery at 15k-10k effort and 4 x 800m @ or just slightly faster than 5k effort w/ 400m jog recovery (becoming 5 x 800m then 6 x 800m). Do 2 days of 8 x 100m @ 400m effort and 1 day of 4 x 200 @ 800m-400m effort at the end of easy runs, with one day of either 6 x 10s hills all out w/ 5 mins easy jog recovery or 6 x 60m all out w/ 5 mins easy jog recovery (alternate).
Week 12: 6 runs, 40 miles, 9 mile “long” run, 3 days of 8 x 100m @ 400m effort, 1 day of 3 x mile @ 10k effort w/ 2 mins recovery followed by 2 x 200 @ 400m effort w/ walk/jog back recovery.
Week 13: Now that you’ve built to an appropriate, maintainable level of different types of aerobic stimulus, you can add up to 1 mile to your long run and 5 mpw total to your previous peak totals every week (still taking a down week every week), as long as you can still do 1 day of 15k effort intervals, 1 day of 3k-5k effort intervals, an 11+ mile long run w/ a fast finish for the final 3-4 miles, and the speed maintenance/efficiency days at the end of most easy runs. If you struggle to hit paces on your workouts, or feel excessively fatigued on your easy runs, or can’t maintain crisp form on your speed development work, take a down week, back off to what you did the last week you could successfully do all of these elements, and know that that’s your peak for this cycle.
Starting in week 9 you can replace any of the workouts with a race of 1 mile-12k, and once you’ve done 2-3 weeks at your peak you can drop your mileage and do whatever types of sharpening workouts work for you, and race 2-4 times over the next month before calling your season a wrap.