There is a long time member/vendor here on the forum "Captainfab" who makes high quality adapter plates and parts for our trucks, and one of the things he makes is a plate that facilitates one to install a PS box onto a non PS frame with out damaging it with hammers & torches.
Here is a thread that shows the plate I spoke of above.
http://www.67-72chevytrucks.com/vboa...632508&page=6t