yes all true the highboy has a low pionon the 77.5 has highpion cost of the d- 60 is 1000-1500 around here...the frame width diffrence is right after the cab... so if you tried to use the 78 rear in your truck you will run into problem you will have to have the spring perches cut off and moved in for the highboy.. so if your buying this for your truck make sure you have the same gear ratio... if they are differnt the rear will not be a direct bolt in (I did the oppsite on my 78)