Be flexible and have fun with it!
That seems to be the way it's playing out, I've picked up a dirt cheap and gently worn K0 cam and just this morning picked up a set of 4 CB77 pistons with wrist pins, clips and rings, all said to be in good shape removed from a stock bore CB750! So this is coming together nicely. But now I'm uncertain if this stuff will wind up on my K3 or on my K8. The K3 has been together with new rings and head on for like 14 years and never been run, it's not stuck but I'm reluctant to disturb it yet and might just finish putting it back together as is since its my first 750 top end rebuild.
The K8 is still apart, HD studs still need to go in and it's been waiting patiently for me to decide whether I want to use the stock pistons and new Chinese rings that came with the basket case, or think up something else. I'm thinking something else, and it rhymes with CB77 & K0.
Now to figure out a wiring harness for it, I'm tempted to just build both bikes with K3 harnesses but I should probably just keep my eyes open for a clean K8 harness.... It doesn't end.