its funny that I must be the only one here that likes the 351/400 for what it is. I helped my neighbor take out a 429 and put back the 351M in his `79 F250. I am kinda the nut case in favor of bigblocks , but when putting them in a 4x4 they kinda get nose heavy. the 460 is 690lbs VS. the 351M 540lbs thats a huge savings when looking and staying a float in deep mud. the other big reason not to do a 351M swap is fuel milage. you can bet your cowboy hat & your house cat that best you will get is 8-10 with a 460 in a 4x4 truck. I could barely get 5-6 mpg in my `85 dually and it was 2wd.