Got this 6.1 sitting (heated garage) for five years or so and finally got to it. Only 27,500 miles (that's what I was told anyway) but had a rod knocking sound after half a minute after start. Found a spun bearing so went shopping and found a crank and rods from a new engine. He was building a stroker on a new engine. Also bought new crank and rod bearings.
Why does it happen and is there a cure?

Cyl and crank on 1,2,7 and 8 looks good, but 3-6 are not so nice.
You can barely feel a couple of scratches in 3 and 4 cylinders.
A honing job should be enough I guess.

Will I have to replace the pistons or would new rings be enough?
I'll try to post some pics.

My plan is to drop it in my 71 Sport Fury and run an A518 behind with 3.91 gearing and 28-29" tires.
Have been looking at a MegaSquirt box to control it. Have a friend who works at a company with a chassis dyno and he's used to working with MegaSquirt.
The car will be driven a lot, but I'm not gonna be too hard on the revs.