This weekend I got the 62 frame drilled and the 72 cross member fitted.
A couple of photos showing the two different cross-member L-brackets with the mounting bolt differences. Rear is to the right in the pics.
The 62 first -
And the 72 -
As you can see the upper holes are the same for both. I bolted up the cross-member using the upper bolts and then drilled for the lowers. The lower rear bolt needed a new hole more rearward than the original. The lower front needed to be slotted slightly upward and to the rear a bit.
Also, since the 62 frame is shorter than the 72 frame, there is a gap between the bottom of the frame and the new cross-member. A shim made from the scrap pieces of frame that came with the 72 cross-member fills the gap nicely.