I have a 67 econoline p/u with a Mustang 5.0 and aod trans. I bought the truck with the engine in and driveable. I did all the doghouse and floorboard mods myself. More about me later, You brought up your rear end, your truck came with a 144, witch means your rear end is a 7 inch with 400:1 gears. My first Econoline was a 63 3 window with that same power train. In order to change the rear end using only wrenches you need to find a 63 Galixy,,,, OR do what I did. I found a 66 super van (funny lookin extended van) I could see from the hiwayand knocked on the door. Many econos came with the Big Block 240 ci 6 cyclinder, and all big block econos came with 9 inch rear ends, usualy with 350:1 gears. If you still have your stock 3 speed, then you need the 9 inch rear, drive line AND the yoke from the trans. I swaped it springs and all, took 4 hours from both trucks on the ground to same. Don't forget the speedomiter cable driver from doner van, this will make your speedo correct with the new gears. I paid $500 for the parts van, sold the rebuilt 250 in the back to an econo pal fore $500 did the rear end swap on my 63 then sold it to buy the 67, and many interior parts for the 67 came from the parts van. Good Luck, Mark in Citrus Heights