I did a similar hike in reverse some time ago. I started from Lundy Lake and hiked up past Burro Lake to the top of Excelsior. From there, I followed the Sierra Crest south (mostly class 1) to the top of peak 12,160+.
Continuing along the Sierra Crest toward Shepherd Crest seemed kind of dicey: (Edit: It was out of my way.)
so I dropped down to the small lake at about 11,000+. I then crossed an easy ridge to Shamrock Lake. My opinion is that the hardest part for you would be the climb from near the lake at 11,000+ feet to the top of peak 12,160+- a reasonably short class 2 slog. I came down the chute that drops straight from the summit in this picture, but there seem to be several other options. The left skyline is the class 3ish Sierra Crest:
Unfortunately, I don't seem to have an image of the slope above Shamrock Lake handy, but I don't remember any significant hardships.
I hope this info will help