I agree that if you're new to the game, then getting your feet wet on a relatively expensive platform to build, like the gen 2 hemi, then having an experienced builder guide you through the process makes a lot of sense( or just have them build it for you).
All that being said, the smallest thing I would build to make use of that 4.50 bore block would be a 540(4.5 bore x 4.25 stroke).
If he already has the 426 top end and is just looking for a cruiser type build, I would just reuse it all. Clean up the heads, get a decent cam........ 600-650hp on pump gas should be a no brainer, or more...... Depending on just how mild the finished combo is.