Since you want to run stock rocker arms, it be worth your time to look up Mr. Sixpack. Bob Karakasian, and his Pure stock builds.
It was mentioned earlier in a post that the 68 Charger would not be competitive in Pure Stock????. Yes it is true, you would not be running with the max wedge, Hemi, and six pack cars. But you will be well behind those cars in F.A.S.T. also, not to mention those cars usually take at least 110 octane fuel, and are stock looking modified RACE cars.
Spending a ton of money on head porting and more cubes, then hitting a performance wall by running pump gas with the factory HP manifolds is going to be spending a ton of money with very little to show for it. On top of that your talking about using stock rockers that don’t survive long over .5” lift, that will not begin to use the flow of a highly ported head.
You might want to consider the Pure Stock build direction (which you indicated your a fan of) over F.A.S.T….. They lax’d the rules some in Pure stock so you can play with the cam a little more. It has to pass a vacuum rule. The engine can run 1.5 higher compression than the factory rating, in addition, lighter pistons, thin rings, H beams rods, fancy valve jobs, are all are updates you can do to the engine in pure stock.