All the info I get says the 416 is 58cc and that's what I've been going by for the past 20 years. If they were 64cc then the compression ratio on a 305 that these heads came on would be dirt low.
Going with a set of camel humps isn't a bad idea, but you have to realize, if you find a set that has to be rebuilt you'll be sinking $600 in them just to bring them to spec. If they need rebuilt they'll need to be magnafluxed to check for cracks, milled to flatten the decks. Also will need valve guides, possibly new valves, hardened exhaust seats and of course the basic valve job. Vortecs aren't a bad idea either by no means. You can usually get a set for around $600 ready to bolt on. However you'll need center bolt valve covers, You will need a Vortec intake, you won't be able to use the intake you have, and you'll need a set of self guiding rocker arms. By the time you add that up, plus the price of the cam and timing set all $1200 will be gone and you won't even have a set of headers for it yet. I suggested the combo I did because it's cost effective to the parts you have and it will help performance. No it won't be a fire breather, but it will have great low end torque which is just what a street truck that isn't going to see any track time needs.