Additionally my '78 had square holes punched in the frame were the bolts went and about a 1-1/2" by 1" hole between them to slide the nut plates into the frame... I had to drill a hole for this on my '71. Also the hitch is made by Valley Industries and has 2 sets of holes to fit pre and post '78 bumper brackets.
Well, I looked at the Valley hitches and they only list a class 2 hitch and I need a class 3. Still looks like it should be easy to adapt the '78. If I need to do some welding, that's ok. Thanks for the info.