All studs stretch, so that's not really an accurate concern. Warpage of the block or head are more likely to generate a leak than stretched studs at this point. The studs were installed and torqued into the block, then nuts to the studs at a design spec, which built into it the stretch factor. Once stretched, they stop stretching due to the limited torque.
Hard to be certain from your picture, but there seems to be some corrosion on the shafts of a few, plus some at the base. I'd replace them purely for durability concerns. At this point they're 40 years old, they're inexpensive parts, readily accessible, and critical for the proper operation of your motor. No other reasons matter in my judgement...