A crock pot with antifreeze works well on pistons and small aluminum parts. I know these pistons are large and it's an overnight process, but they will look like new.

One a day for four days, are you in a hurry?

Thanks for the replies. I got the v6 back together and itÆs running good. I cleaned / buffed all the sensor connections on the back of the intake manifold to resolve an electrical problem.
Cleaned the metal hose where it bolts on to the block underneath the intake manifold which had been leaking antifreeze and that seemed to fix the gurgling noise I had on startup. I buffed and clean most of the hose connections elsewhere.
I honed the engine while it was in the truck. I removed the front diff so I could see better and clean up the bottom of the block more easily. To stop honing crud from getting in to the crank oil holes I used ear plugs to block them off plus a lot of rag towels above the crank. To clean the cylinders I used about 1 1/2 cans of brake cleaner per cylinder. Be careful where you spray it because it started to pull oil out from the main bearings and the crank got hard to turn. After cleaning it up I put the new re-machined heads on it and put it back together with new rings and bottom end standard shells. I charged the crank oil holes with Lucas oil stabilizer as the bottle fit in a cylinder and the nipple on the bottle fit in to the oil hole on the crank. It was a lot of work but I've got 900km on it now. IÆve changed the oil twice and it running great. No more thumping noise, no more gurgles and its running fine.
I know - itÆs a long post, thx for the replies.

You can use anti-freeze and a crock pot.

I use it to clean small RC engines.
They come out looking like new in about 8 hours.

Just drop the whole thing in and they come out looking like new.
It not only removes the carbon it really cleans the metal.
A day and a half and you would be done with no scrubbing.

You did save the old fluid? Thrift store and $5.00 gets you a crock pot.