I installed just such a bracket on my 78 SC instead of the heavy steel one that was originally on my car. There is a removable bracket attached to the cylinder head held on by two bolts under your fuel rail. From the front of your large bracket in side the small rectangular opening there is an 8mm Allen bolt that secures the rear bracket to the large mounting plate. Try removing that bolt and you should be able to lift up the main mounting bracket. I hope that this makes some sense...
