Cudafied makes a good point. Don't build a house on a bad foundation. It will be much cheaper in the long run to go with a new aftermarket block. If you sell the 440 block you have, then figure the cost of machining, subtract that from about $5500 you will come up with the difference to move up to a KB block. That will make for a rock solid foundation. Subtract from that balance what it would cost to redo a stock rb that cracks, and the picture looks a lot better! With a KB or other block, go 4.500 bore and at least 4.25 stroke. Don't worry about being close to the limit on the bore of the block. You can get several rebuilds out of the 4.50 bore, and once it gets worn out to say 4.502, just order pistons for that bore size. I doubt you will exceed the life of a good block starting at 4.500.
If you go with a low deck, use aluminum rods and very light pistons with a 4.25 stroke 2.200 journal crank, your bob weight will be very light. If you need a crank, find one with center counter weights if you can. It will reduce internal stress a lot. If the heads haven't been ported, they will need the full treatment. A good set of rockers, like Jesel, are a must due to the springs you will be running. Most combos making 850+ hp will need a lot of cam. Somewhere around .750 intake lift or more, with about 280 to 284 intake duration, 284 to 290 exhaust duration set somewhere around 110 CL. The jesel rockers listed at 1.5 are actually 1.55, and I made over 850 hp with the Isky RR735 cam as an example of what works. If you have to start fresh with the valvetrain, do it right and get a high ratio intake rocker, like 1.7 or so. It allows you to pick a lot more lobes that will work. 2 1/8 x 32 x 4 inch headers are what I had, work well. A good oil pan is important for keeping crankcase windagedown, makes more power. Run a vacuum pump, set 10 to 12 inchs. Top it off with a dominater or injection on alky, and you are good to go.