What about the frame?
It will need to be longer. I've read a little of your 1st post( about advice for your 64) but didn,t keep up with all of it or what your final thoughts are.
I would not make it to dificult or you may not finish. Make sure you have fun with and it will always be your truck personalized in your own way.If you truly want extended cab go for it!
The skys the limit and everything is possible.
Ken
