refresh my memory....the 260's are sort of MW size?

what intake would you be planning on using?

that big cfm gain on the heads would get noticably reduced once you bolted a std port M1 onto them.
on the other hand, IMO the large cross section MW manifolds like a 440-2 will hamper how well the motor hits the converter with the stall speed you're running.

FWIW, i wouldnt be looking for 600ft/lbs out of that combo on our dyno, but i wouldnt be shocked at 670hp(depending on what the intake manifold choice was).

that EZ295 headed 448 i built a few years ago made over 680hp with the same CR and cam that you have, but only made about 560tq.