I thought it was '74, but you could be right- I'm never wrong, but sometimes I make mistakes... :)
Okay, did a little digging, seems '75 is the first year for cats across the board, but I see some conflicting information on whether Cali got them a year earlier, and/or whether some '74s may have already started getting the different floor pans at the end of the model year... I dunno.
OP, maybe the buckets will just drop in. Maybe you'll have to do a little finagling. I'd give it a shot.