If you haven't already seen it, take a look at the video referenced here:
How to Build a 3.8L Porsche Track Monster
Maybe jump to about 8:20 and 12:00 to highlight some key points.
That shows
all new parts going in, but makes me wonder if you can add in a new single rod and piston to the engine if you rebalance all of them across the engine.
There are used rods, but good idea? I don't know.
***EDIT:
A quick read on cracked-rod design/cracked cap technology makes me think that installing a used rod or even reinstalling your old rods/bolts is probably not a good idea. Look at some of the aftermarket products. They are probably better and cheaper than OE. ***