Unfortunately the FAM doesn't cover the earlier years (or anything about the pickup beds for that matter.) The GM documents are either lost to history or the publisher of the FAM (not GM) only collected the later drawings.
If you have the grille assembled, it's pretty evident where the connections are. IIRC there are u-nuts along the bottom edge of the grille bar to the front of the lower splash apron. There might be one u-nut on the upper edge, but I believe the grille has weld nuts for the most part. I know there are 3 weld nuts on each side of the grille that get machine thread bolts from inside each fender along the vertical edge.The two heavier tabs extending backward from the lower splash apron attach to two weld nuts on each side of the radiator support.Those bolts go thru the inner fenders.
If you disassembled the grille by drilling the tubular rivets out, there are bolt kits to replace the rivets. The bolt heads are like carriage bolts but without the square under the head. That's the way I went. Here are some pics of grille disassembly and reassembly.
THIS POST shows disassembly and the notches for matching up the inner and outer grille bars. And
THIS POST has a couple pics of grille assembly.
Feel free to shoot me specific questions on assembling your front clip. I put mine together on the frame with a helper. Starting with the radiator support and working out from there.
