If you have wing vents you may not be able to leave the doors on with this method. I used the exact wood contraption that rhodog77 used and it didn't work on my 53. I even tried ratchet straps to keep the cab from tipping forward, but it still didn't work. Then I tried with the doors open so that the wood would sit further forward, but I think it was the weight of the doors out in front that caused the cab to roll forward.
Here's the whole story about what I did....
http://67-72chevytrucks.com/vboard/s...d.php?t=385689
I found that the under dash mounts at each end are very strong. I used them to tie off in front and used the hole that's almost center behind the seat riser for a rear mount. Worked real well for me....
