Knocking noise?

[brothers69c-10]

I finally have my 78 k10 back on the road with the 427 tall deck. I completely dismantled the motor and put all new bearings, gaskets, cam and lifters, timing chain set and new push rods in the motor along with honing the cylinders cleaning everything up. Now that the truck runs and drives i have developed a noise that sounds like a knock or chattering. I first noticed it when i drove for the first time. the noise only came about when the engine was under load goind down the raod. it could not be heard idling or even when putting the truck in gear and holding the brake while giving it gas. it originally sounded like a rocker arm chattering so ifigured no big deal put about 50 miles on it then readjust all the valves. Now its got the 50 miles on it and the noise has progressively gotten louder and can now be heard while idling. Also it now sounds more like a knock. If you give it some gas it will sound more like a rocker chattering while going down the road. I crawled under the truck while it was running and the noise was louder underneath and almost seemed to be coming from the bellhousing area of my transmission. I have checked for exhaust leaks and have none, there are nos signs of metal or any contaminants in my oil, and all my other fluids have been topped off. the only other wierd thing the truck is doing is that when you put it clear to the floor it starts shaking real bad and won't exceed 2800 rpm's. I'm sure that part of this is due to the kick down not being hooked up, but it did the same thing with the last motor that was in it only worse cause it was a heftier built motor. I'm afraid to drive it too much for fear ruining something. I've already dropped a ton of money in this darn thing and can't afford to put much more in it right now, but we could really use an extra 4x4 around the house. So if you guys have any suggestions i would be happy to hear them and will try to provide all the information i can.