1963 Rambler American L-Head Tick

That marble rolling in a can might be your throw-out bearing touching the pressure plate fingers,  you might need to adjust a little more free play into your clutch.

The first thing I'd do is pull that cover plate/pan off the bottom front of the bell housing. You can clearly see the clutch, so check every bolt holding it to the flywheel for tightness. You can rotate the engine with a wrench on any of those bolts. Tighten all of them. You might be able to reach the throw-out bearing. If you can,  reach up and turn it. Since clutch is "out" the bearing should barely touch the clutch "fingers". You might need to loosen the clutch adjusting rod to release enough pressure to turn with your fingers. If you cn turn it, it should turn smoothly. If not, it probably needs replacing. You can pull the trans back and leave the bell attached to change that or the clutch, that's why it has that big pan shaped cover. If you go that far, look at the clutch and see how thick it is. Should be about 3/16" thick on each side (the wear "padding" on each side of the metal plate in the middle). If it's 1/8" or less I'd get a replacement. 1/8" is still good for a long time though, IIRC. 3/16" is probably a new clutch... been a while for me with a clutch!

You can easily pull the oil pan on a 63 American engine without pulling the engine. The K brace comes right out and the steering drag link easily comes off. I advise using jack stands on the body just behind the wheels (under firewall) or well out in front under the bumper mounts rather than anything supporting the wheels if you're taking that K brace out. The "frame" can expand under the engine -- the only flaw in the design. It DOES expand over time, but we're talking about a 55 year old car! Even my first 63 was 21 years old in 84 when I got it, and had seen a lot of miles. After 10+ years on the road they start to spread a little. Mine had spread enough at 21 years (was originally mom's car, then went through two teens before I got it!) that the stack of alignment shims was about an inch on one side, 3/4" on the other. Should be only about 1/4" stack on each side, so about 1-1/4" spread. My solution was to weld a piece of 1" angle at the bottom of each suspension mount, cut a piece of 3/4" pipe the correct dimension, then use a piece of 1/2" rod threaded on each end to pull it in. Worked great, and could easily be removed if I needed to get the pan off or engine out (engine was designed to go in/out from the bottom, real hard to pull from the top in those cars!). That K brace helps, but doesn't hold it in good enough for over 50 years of use. With only 36K miles yours may be a lot better than mine -- it had over 100K, engine and trans had been rebuilt around 85-90K.

Thank you as always for the excellent thoughts! I have tried to put to my ear on the dipstick this afternoon like you said and I could not hear anything down there as well as using the stethoscope i hear nothing in the lower end. I do notice that the knock is coming from that #5/ #6 cylinders area. So my next plan is to double check and adjust the valves once again, then i will remove the head and check the valve seats (since i don't have to remove the engine to do so)! 

vinny has some good advice! Pour a little water down the carb while it's running, with your hand on the throttle to keep it running. Just dribble it down. Could be carbon holding a valve slightly open if you're lucky.

Getting the head off is a chore! I'd spray the studs good with some kind of penetrating oil... PB Blaster is something that's good and you should find locally. Kroil would be better, or mix 50/50 acetone and tranny fluid -- that seems to work best, but keep it in a sealed container when not used  as the acetone will evaporate eventually. The nuts will be easy to get off, then soak the studs over night. The studs rust around the holes, and if it's never been off (very likely!) it can be a bear! I had to resort to a steel wedge to get the first one I took off away from the head! That's a bit drastic, but it worked with no damage to block or head. Worked it around a little at a time. If the studs will come out after a good soak that would be the best way, but you still may need to drive a wedge or screwdriver in to break it loose. Try the starter first -- compression will sometimes break the seal, but not if it's rusted in all those stud holes.

Maybe the T/O bearing is getting worn out or sticking or you've got some noise happening in the transmission. Can you see or hear anything from underneath with engine idling in neutral? It's been quite a few years since I had a manual in mine so memory is foggy on what you can see. Any difference in sound with foot on the clutch and in gear or wheels up and turning in gear?