Okay I think I have identified your bracket. Believe that is for the US market 1/79-7/80. That one splits into two smaller pipes and runs under the frame where the CAT is mounted below the driver's floorboard. Not even sure my 3/79 still has it. Does have the stock pipes which surprisingly are...
I have a 10/75 (76 model) and a 10/79 70 model with a very early 2F installed. Neither are here and can't verify the bracket. The two early 2F I have in sixties cruisers both have been switched to headers. I switched my 68 to a header years ago but kept the stock manifold and switched back...
Was that on the four speed bellhousing you bought for the three speed to four speed conversion? Doubt it's aftermarket with that stamped rib. May be from a different vehicle.
Do you have the bracket show in the diagram already. In my pile of exhaust parts have two first section of exhaust that...