Way back in the dark ages I bought a new 1976 Trans Am. First thing I did was to put 15x10 Keystone with BFG 275 Radial TA tires in the rear and 15x8 with 215 tires on the front. Looked great but ran like a pig with only 215 HP out of the box. Next came a set of heads from a '68 GTO that raised the compression ratio from 7.6 to 10.5 along with an Edlebrock intakes and a completely reworked Qjet carb. Then I got a 12 bolt posi with 3.73 gears from a 71 Camero and swapped that in replacing the 10 bolt with 2.71 gears. Now we were getting somewhere. Finally went all in with a 4 bolt main block Milodon studs, decked. aligned bored, punched over .60, Cut down crank. forged rods and full floating pistons with a custom cam, ported the heads. Milpdon head studs, and Crane Roller Rockers and Hooker Headers. That took me to 500HP and remained more or less what I ran for a decade except for the cage which came a bit later after the engine build.
This came out in '79 and stayed in my car the rest of the time I owned it to be joined by the next one 4 years later
Now to come clean I was a bit of a cheater. Pontiac blocks from the 326 to the 455 were all the same physical size so you couldn't tell what size engine it was by popping the hood and looking. However, if you had a flashlight and knew the right angle to hit the block the engine size was cast on the block. Now Trans Am did come with some of the hottest 400 Cuin engines from 1969 to 1972 so it wasn't uncommon to see those in a car. 421, 428 and 455 not so much. We would grind off the 455 and stick weld 400 in it's place , clean it up with a Dremel tool rub some dirt and oil on it and now nobody knows you were running a 455 or a 472 in my case.