I did the same thing to my '71 350. Except, I used wrenches to take them off!
Most of the time, I just guess at my speed. But, if I want to know I'll put my GPS on. You can see the handlebar mount in that pic.
I'm not too concerned about most of the lights. But, if my low oil or over temp lights aren't working, I fear cooking my engine. I can live without the rest.