That's a stretch, the 481988 casting 400 block was first cast in early July of '70, for '71 model use. the 481988 casting 400 block was cast for use into the early into the '75 model year, then its use was discontinued, replaced by 500557 400 (thin main webbing) block.the gm block casting # 481988 was used on 400 engines from '67 -'78. you gotta have the the 2 letter code up front n casting date to ID a Pontiac engine.
that's what my cylinder head/block ID guide says. AUTOMOTIVE ENGINE REBUILDERS ASSOCIATION. COPYWRITE AERA 1981. I worked at a auto parts store / machine shop in the mid. '70s. this book was our bible for identifying heads n blocks for ANY American engine, not just Pontiac. I looked in another old book I have n it says not till '71 like you said.That's a stretch, the 481988 casting 400 block was first cast in early July of '70, for '71 model use. the 481988 casting 400 block was cast for use into the early into the '75 model year, then its use was discontinued, replaced by 500557 400 (thin main webbing) block.
For the '78 model W72 400 blocks, code X7 and WC, the 481988 casting block again began being cast in the late summer of '77. This time it had an XX casting in the valley area, and only 3 bolt bosses tapped for clamshell enginge mounts brackets. The casting of the W72 blocks continued for several months up into April of '78. The Pwh coded 400 4spd blocks for '79 400 4spd T/A's and Formulas also used the Late casting version of the 481988 blocks. Every Pwh block I've owned has been cast in late Sept or Oct of '77, which jives with them being stockpiled for '79 usage.
As mentioned, all 400 blocks used in '76 and and '77 were 557 blocks, including the '77 W72 engines. So, I can't see any 481988 blocks being cast in '76. Then, as mentioned, the '78 & '79 W72 engines used the XX481988 blocks, with only 3 motor mount bolt holes. All the date codes on these blocks, which I've seen are from '77. I've read that no Pontiac 400 blocks were cast after '77. Can not confirm. But I've never read of anybody who has seen a 400 with a '78 date code.can you make sense out of my date stamp?