How much will adding 16 lb to my car affect ET/mph(rotating weight)

Agree.
have a built drive shaft, can't remember the u joint sides but had to get a new Pinion yok because of it.
Have a drive shaft loop, and run slicks most of the time. 28 10.5 15. Which is why it's going to be a challenge to make a 215 70 15 hook.