After looking at the balancers on the pontiacs outside, I cannot tell a diffrence between the 350/400/455. My guess would be to go to a junk yard and look for an old full size pontiac or grand prix with a 400 or 455 and pull it off .You can tell which motor it is by head number castings which are usually still visible, and the firebirds at junk yards usually dont have engines but can give it a shot. Might check ebay too... be sure to replace that front seal while youre at it, pretty sure the seals are cheap.