The frames are pretty different between the 67-72 trucks an a 73+. The large "hump" over the top of that crossmember for driveshaft clearance will hit the cab floor. If you trim it out then the drive shaft will hit it if you going to be pretty low. Another problem will be spring/bag mounting as the pocket for either winds up outside the square body frame.
I have the porter built kit an I honestly would NOT recommend it. Get the CPP kit instead, the part number is 7387TAC-A and it's 1199. I don't know that it's any better but the problems I've had with my kit have killed my motivation for working on it an it's just been sitting for almost a year now. Not much free time an low funds haven't helped either though
There's honestly no low buck way to do without putting so many hours of work into it that you don't come out ahead or with a better working product than one of the available kits. I think it would be easier/faster to adapt a 73+ body to a 67-72 frame than try an make it work on the stock frame.
These are just my opinions though, porter told me several times they were improving parts of their kit that I was having issues with. They might have as I quit asking after a month of getting the same "I'll have details for you next week" answer everytime I e-mailed. I've never heard anything else about it or if it's supposed to be better. I'm not the only one that had trouble out of that kit either.
