Why saddle yourself with the stock block? I have never, will never understand this. Get a Dart Little M or an SHP block. Throw down at least 396 cid. up to say 427cid. This gives you room to grow (I believe up to 454)
Save the numbers matching stuff for garage art until you sell the car. If you chuck a rod through your numbers matching block....good luck. Paint your little M block orange and 99% of people would never notice.
Yes its more money; the motor will have better manners, make more power, be stronger and give you the peace of mind that its not going to come apart at the seams. Good seasoned blocks with minimal coreshift are getting hard to find these days; and you want to avoid the thinner castings.
Or you could find a boatyard and get a 502 mercruiser motor; change the cam and intake and get awfully close to your goal