Switching to a 72 clip

Do i still need the hood latch support brace that connects the bottom of the latch to rad. core support, if I have the steel insert that goes under the grill on a 72?

Yes. You'll want it to keep things stiffened up.

My only problem is that the support brace that I got is hitting on the bumper filler panel and the back of the grill? I think that I may have gotten the worng one.

Sounds like you have the wrong one. Check the part number, you may have one of for a 73-74. Unless your running a lift off fiberglass hood, you will need that support.