The mark is to help ensure all p's are installed correctly--rod attached to crank where oil can enter the hole and lube engine. If there of yours do not have the mark, then maybe that engine was rebuilt in the past and they reused 3 of the old pistons and replaced 3 w/o the mark. IMO, for balance sake, it is ALWAYS best to have a complete set of identical p's.

A large part of building/rebuilding these engines is doing research, knowing the parts and why they are as they are. Use google, Summit Racing, ebay, etc. to get info too.

 

Ditto. Reference my earlier post about the "Professional Rebuilders" using castle nuts on some rods. I bet the motor those came from had been gone through before, most likely by one of these outfits. They take my philosophy of re-using any viable parts to a perverse extreme ( frequently using parts that really aren't viable - like whatever nuts are laying in the floor) This would likely extend to pistons as well. I can't imagine anyone using anything other than a matched set. Anyway, they are the exact same mark as mine. I remember very well just a couple of weeks ago when I was cleaning and inspecting mine to see if they were usable seeing that very mark. I couldn't help but think when I saw them that they seemed unusually large. Pretty much every piston has something similar. Some are small and difficult to see. They might be on the face or the pin boss Read the rebuilding section of a Haynes or Chiltons manual and it will show you where they are and that particular engine's method of making sure everything goes together in the proper orientation. I assure you that's what we are seeing in your picture. As to the mixed up pistons, the above is the best attempt at an explanation tha I can come up with.
What about the engine that they came from? Do you know the story on it? Did you tear it down? If you have it sitting around then it might be a viable core to rebuild.

 

im going to pull the head off tmw and post some better pics of the pistons

 

took the head off tonight and your right they are placement marks, and all 6 pistons have them all facing the same way. i did notice on the pistons there was black residue caked on the pistons, looked like residue on the bottom of a leaking oil pan thats been leaking for about 5 yrs and shi t builds up and you run your finger through it, thats kinda what it looks like. also at the very top of the cylinder wall there is a ridge/lip with a black ring around it. I sprayed the pistons down lightly with some cleaner and it seemed that the liquid ran right down the cyl walls past the pistons because when i would rotate the crank to bring the nxt piston up to clean i could see liquid on the cyl walls, as it was goind down? I dont know im just rambling on here. Will too much gas cause the engine to smoke another color than black. like a grey kinda?

 

any takers

 

If the tops of the pistons and cyl walls are that covered with carbon, I'd bet the rings are gone. They could be worn out, stuck, or broken. It's also possible they were installed wrong.
At any rate, it's prolly best to at least pull the pistons out, and replace the rings.

Too much gas will make an engine smoke black, but if left running that way too long, the rings can certainly take a beating, along with any other parts that rely on the oil to lube them. The gas can cilute the oil, increasing (dramatically) the wear rate.

 

If that's just carbon at the top, you MIGHT get away with a 'good-ol-boy' hone and re-ring, but if it's actually metal, then I can tell you without even putting a micrometer on it your bores are shot and will need an overbore. Either way, sounds very much like what I said before, your rings, at the very least, are toast. Sorry, I know no-one wants bad news, but that's the straight of it. Had more than my share of bad news on my own lately. For the first time ever I had something break when I had a little money to work with. Now, however, I'm over budget on the engine, (back to broke) and need a tranny rebuild. I'm wondering if there's a Pull-A-Part or similar junkyard in your area? I got a 300 from the one here last year. Engine, tax, & core charge (kept my old one to build) came to less than $200. All I did was clean it up and replace some gaskets that were leaking. Dropped in and runs, no smoke, no knocks. Can't complain about that. Take comp tester with you, find or borrow a battery to turn over and test before you pull. Check for obvious stuff, (not locked up, has oil in pan, but NOT water, etc.) Be smart and careful, and you could come out. If nothing else, something to get your truck around for a while so you can slowly collect parts and get machine work done as you are able, is good. I've driven around a beater engine while building another on the stand as I could afford to more than once. Saved money, bought parts, etc. for TWO YEARS on a SBC for my Laguna when I was younger. Worth the wait too. I built a MEAN motor for that one!