Do you have a pic? Previous owner pulled the 350HO and dropped a 400 in and rerouted a lot of the wiring.
I only have an old picture, but the fuse seems to be hidden behind the thermostat housing in the picture. It is the wire incircled in red I'm talking about, running from the alternator to the high speed relay (incircled in blue).
The air cleaner is from a GTO, so it is not correct for a Firebird.