The 250 is not a bolt-in swap.
The Holly Sniper will work fine on your 216 but you won't see an real performance gain according to those who have installed it.
I drive my 216 3spd in rush hour, freeway traffic every week in Atlanta. I just stay in the right lane and putter along. Shifting gears when required doesn't bother me. 55-65 on the open freeway (still in the right lane).
