Rowdy and Mean 318 build

Same rods

If you plan on turning 6500 you need to do some oiling mods so that the rod bearings will survive.
And you will need some serious valve springs. With that comes a special break-in procedure and the battle for just the right amount of ZDDP so the lifters will live. You're gonna need a lot more cam than the 268 to hit 400hp, and that means a lot more rpm than 6500.And a lot more compression.And a lot more stall. And then a lot more gear.
But the 268 is a fun cam, when the compression,the TC, and the rear gear, support it. So are you willing to give up the 400 target?
The 268 in a teener will power peak at about 5400rpm, and with a 904 will want to be shifted at about 6500 into second, to drop in at 3850. You will need the oiling mods. This cam will not be satisfied with the 2600TC unless the compression is pumped up. Even then it will be iffy.
10.0 will be your Scr target, for a Dcr of [email protected] will need to get your TOTAL chamber volume down to 73.2cc.
She will want 3.91s with that 2600TC. Probably 3.73s with a 2800TC and over 3000 with 3.55s.Each of these gears is about 5% apart, and so you will need 5% more torque to happily run each lower gear.
DO-NOT-OMIT the oiling mods, unless you have deep pockets for a do-over.
Forget 400hp with a teener, it's just too high/expensive a target. This 268 will be big fun when properly supported. If not supported it will be a big fat do-over.

If you really want 400hp,rebuild that 360. Same money gets you 13% more everything. That 400hp still needs rpm, but now it is doable. Just remember you don't get it until about 5800rpm, so with 3.55s, that is about 54mph. The cam will now want to be about a 284*, and will want to be shifted at 6800 with that 904,going into 2nd, to drop in at 4000. The 360 will want lots of compression for that cam, but it's a bit easier to get. And of course the oiling mods are still mandatory.
You can go down 1 or even 2 cam sizes ,and 3.55s are just right.With enough compression the 2600TC will hang in there.