" Not going for numbers here...Will go for period correct tho..."
OK, I assume by "period correct" you mean '67-'79, which was the period of time, when the 400 was used in Pontiacs.
So, a 400 block from '67 thru early '75 will work. Beginning during the '75 model year, when the #481988 blocks ran out, they began using a #500557 block. These blocks had thin main webs, which proved to cause a lot of failures.
They did make a stronger 400 block for '78 &'79--# XX 481988. But these blocks had only 3 of the motor mount bolt holes drilled and tapped. So, you cannot use these blocks in your '68, without some sort of motor mount adapters.
I'd recommend using a '71-'75 casting #481988 block. They were used in all '71 thru earlier '75 400's. So, they should be the most plentiful, good, 400 blocks still out there. Yes, any of the '67 thru '70 400 blocks will work in your '68. But, if you build with one of the '70 thru early '75 blocks, which had all 5 motor mount bolt holes drilled and tapped, the engine will be easier to sell, should you ever decide to sell it. That's because it can be used for either 2-bolt or 3-bolt motor mount applications.
For heads, I'd use the '75-'79 # 6x heads. The 6x-4 heads, that came on 350's and W-72 400's, had smaller chambers, which will provide a little more compression. But if you don't really want a high performance engine, but just a good, very pump gas friendly, daily driver, you can use the more common and cheaper 6x-8 heads. The 6x-8 heads provided only about 7.6:1 compression. But, by milling off a small amount, using thin Cometic head gaskets, and a small Voodoo cam, you can build a spunky little pump gas 400, which will make a good DD, and will burn rubber, when you pop the clutch. :lol:
To, further look "period correct", I'd run a 1972 iron intake, and a good rebuilt '76-'79 Q-jet carb, with an electric choke conversion. But, of course, if want it to look more period correct, for the '67-'69 period, you can run any of the '68-'71 heads and intakes, and a '68-'70 Q-jet, with a divorced choke. Some #16 or #62 heads would look right on a '68 Bird. But if the chambers are 75cc or smaller, you need to use dish pistons, to reduce compression, for pump gas.The '70 #64 heads would look close enuff, and would be my pick from those years. The '71 #96 heads are also good heads for a low compression 400. Even the low performance '68-'70 2-barrel heads, such as #17, #47, & #11, can be used, but will need to have screw-in rocker studs installed.
Well, as you can see, there are LOTS of ways you can go, depending on exactly which "period" you wanna be correct for. But this will at least give you several ideas of possible ways you can go. Good luck with your build, whatever you decide. :smile22:
