71 Pontiac FireBird 400 Big Block

So someone educate me I thought Gm's 400's were small blocks, replacement for the 350so I looked it up and apparently they have 2- 400's some are small blocks and the 6.6 is considered a big block, soooooooooo anyone know whats what?? obviously I am not a GM guy... from wikipedia:
Engine development: small-journal engines: 400 For 1967, Pontiac introduced the 400 cu in (6,555 cc). The '400' V8 was essentially a bored-out (+.060) 389 with 4.1225-inch (104.71 mm) bore and 3.75-inch (95 mm) stroke 400.4 cu in (6,561 cc). It replaced the 389 in 1967 and remained in production through the 1978 model year.The 1979 cars with a 400, had an engine produced in 1978

Pontiac HO engines: 400 T/A 6.6In 1977 the 400 cubic inch T/A 6.6, (RPO code W72) was created to fulfill the vacuum of the lackluster 76 455 HO, with improved flow cyl "6X" casting heads borrowed from the 350 yielding higher compression, specific camshaft, 3.23 gearing, and a new dual muffler exhaust making 220 hp (160 kW), providing the Trans AM and Formula Firebird with a breath of new life after some dismal performance years