Visual of the Moog 8228 coil springs this is the exact replacement spring for many F100/F250 from 67-79 although it is not the big long spring that some later model heavy duty F250 7,900-8,100 GVW with tall spring buckets . These measure 15 3/4 " long and the thickness is 0.69 passenger and 0.66 driver side these are a constant rate spring.
Note : Moog description says for 6,200 GVW and under my 69 F250 camper Special is 7,500 GVW and uses this spring with exact height and thickness .