Snakehunter Rebuilding the block is not a problem. Since you are going to bore the cylinders and have custom pistons done, Can the jugs go .015" to clean up? 4.265" is doable with cutting down the rings to fit. This will give you 3 more rebuilds on the block with a .030",.045".060". As far as size of motor, you will need something in a .575" lift to just cover the extra cubes of the motor. I run a crane small hydro roller camsaft in a 482 motor and think this would be also right up your ideas for a great motor. You have to realize that torque moves the car no HP. This cam in my motor is just under 600 ft of torque. It's over 400 from 2,000 to 5,200. HP is in the mid 540's at 5,800 rpms. Car has a little lope in the motor and will idle at 775 all day with out any issues. Blows the tires off in first 2 gears. What gearing and trans are you running?? I am only running 10.5 compression and premo gas at the pumps. 91 octane. The cam specs are .587-607" with 6 degrees retarded. I am going to advance it 2 degrees to kill some of the torque in the bottom end. Max rpm is 6,500. I run a chip of 6,200 in the MSD. Tranny gearing and rearend ratios are what will effect how the car runs. I have a 5 and 6 speed for the car with 3.31 gears. I may switch to a 3.07 ratio. Both tranny have 3.00 first gears and .86 over drive in the 6th speed one. This is for big tracks where she can stretch her legs. Limit is still 135-138 mph, but it's how you get there that's the fun.
Your motor looks most surface rust. boil clean it and see what the machinist says about it. Find a pro machinist that knows how to build aluminum motors.
1 side note. If the manifold has not be ported, send it to Joe craine for one of his great port jobs. He makes all the port flow within 5 cfm of high to low. The stock manifold can be as high as 30 cfm out.
If you want some more info, send me a P-M. Rick L.