Here is my take on the frame situation..... as I to needed one. I sourced mine from a 65 malibu SS. all 64-67 frames are interchangable w/minor modifcation. the converts,vista wagons(glass roof)and elcaminoes had boxed frames. as well as a handfull of HT's that had the HD frame option. this includes the GS as it was a rare option on that as well. Each year and model frame has its differances most of which were at the four corners. the frame horns were different El caminoes and wagons were longer in the rear. and Chevy Pont Olds and Buick each had there own horns as well. any of this can be changed with minimal fab skills and a welder. good luck on your quest
Edit: with 67 having very visable differances throughout but it will still fit