Is it okay to only do LSD for base training?

nothing wrong with doing some acid, just gotta measure the doses. sometimes the best trips can happen while you go for a run if you take a full tab. would recommend microdosing for a track workout tho

in all seriousness, mix in some variable pace runs. try closing your long run at a healthy pace, for example. also consider dropping your easy run pace 10-20 secs per mile, saving your legs so you can make the medium long run a more purposeful run rather than a mileage builder. could make it your weekly fartlek.

are you doing strides/buildups after each run? have you incorporated hillwork yet?

then again, if its LSD, your easy days are probably pretty easy. Listen to your body - if intensity gets you in trouble, get creative with how you approach it. hillwork, grass field sprints, mini fartleks, etc etc. examine your running surfaces and shoes as well

Thanks for the suggestions. I'll try closing my long runs well, but it might be a few weeks as they still feel really long due to the mileage bump.

I haven't done any strides, build ups, or hills so far. I don't have time to do strides after a run in the morning before work without sacrificing core work, stretching, or sleep. But I like the idea of working them into a run, like build ups. I might try that.

Just add in strides the last 10-15 minutes of your run. Something like 6x:30 on, :60 off etc

You really can't double? That hurts my soul. Even if you could add in some 2-3 mile runs in the night, it would help. I think you should add in some mild quality, like modest tempo runs, strides, and reps @ 2 mile effort.