440 blocks are usually stronger than 383 blocks but 400 blocks might be better than either. Hard to say really with any certainty. This stuff is all 40+ years old.

More cubes and less compression might be the ticket. A 4.25 crank in a 440 builds a 505. With 6.80 or 7.10 rods you have a super nice bottom end and plenty of room for a dished piston to get you to 10.5 compression. You can change the gearing and run lower engine speed while still having the same basic power and same ET.