The slant window frame came out along with the vicky.
The two major changes are 2/3 bracket for the rear of the cowl were moved rearward such that front hole now lines up with the rear hole on the straight window cowls. There would also be 3 holes just ahead of the rear running board bracket (2 at the top one on the bottom) for riveting the #6 frame mount on the frame. This was done on the line so only slant bodies would have frames with the #6 bracket.
The correct frames are much more available then you might expect. The easy thing to look for is the 3 holes in the side of the frame for the #6 bracket. This can even been seen in small ebay pictures if you know to look for it. Once you know what to look for you will see these frame all over.
Getting the #6 bracket is not always cheap. Frequently they cost in the $80 to $120 range. Bert's knows about them and sometimes have them available.
More #6 mount bracket info click here