You chevy guys have problems we flathead users don't. I think a Z made some where around 180- 200 HP. It doesn't matter how many cubes you have, if your target range is close to that HP number those carbs should work good beacuse you can only mix so much air with so much gas. They might be a bit too much for a 251 Mopar; they only flow as much air (in stock form) as a honda civic (but it would be fun to find out!).