If you have the custom front kick pannels you would install from the outside 6" speaker nut on the inside, then pop on the grill . Without any more info thats all I have for you. If you have the stock kick pannel I believe it would be the same you have to have the speaker exposed to get the grill on.
If you mean factory speaker pods for a 67-68 they mount from the inside through holes under the kick panels. They have to be cut first. The right one requires you to remove the heater or A/C box to get the pod in.
Thats my fault....it's a 67 with the cut out's for the kick panel. Thanks for the info....the car is stripped so the a/c box isn't a problem. It's going back together and wanted to mount these before putting the fenders back on or a/c box in depending on which they mounted.