A '70 Bird 10-bolt will still be an 8.2". If that's what you want, great. If you never plan to run sticky tires, an 8.2 will probably be just fine.
But if you want a stronger 8.5" 10-bolt, you'll need a '71-'81 F-body rear. The 8.5 out of an X-body will bolt right up, without moving the perches. But, an X-body posi rear might be hard to find.
The Summit 2801 is probably the cheapest decent cam for your set-up. It's a higher lift version of an 068.
Would not recommend a single plane intake on a street 400. Either a stock iron Q-jet, or a Performer would be better for a mild street 400, providing more low & mid range torque. One of these 2 dual planes, along with a well built & properly tuned Q-jet, will provide MUCH better street manners on a mild street 400.
Would not use cast pistons, ESPECIALLY the "8-eyebrow" type. The SP L2262F are the cheapest decent 400 pistons.
I would not use those #15 heads. I'd go with 6x-4 heads. You can shave a little off and get the compression above 8.5:1. Or, you can run low 8's CR & run a Voodoo 262 cam, if you want a bit more cylinder pressure.
I'd have one piece stainless valves installed, along with bronze guides, and a GOOD complete valve job, done by a good head guy, with experience doing performance Pontiac valve jobs. 1.66 exhaust valves are just fine for street use. SI sells the short 1.66 exhaust valves. Part #6001SG.
