they had those forearms in the late '70's, I had one. It doesn't much matter when it was made, the condition is what sets the price. You can buy a new one for $1200 or so, here's an ad from Goble's for a new one
T2042 Browning BT 99 12ga 2 3/4" Singl Barrel Trap Inv Plus Reg. $1249.00 $1,149.00