I have not rebuilt a 304, but I have rebuilt a 360 AMC engine in my old 73 Wagoneer.
AMC individually fits the Crankshaft Bearing at the Factory depending on how the crank pins and journals measure.
Unless your Crank was ground during the rebuild and ground to a next std. size .010" ,.020" undersize with new bearings, you may be hearing a little rod or main bearing noise.
You won't hear it too much when it's cold, a little more "Oil Cushion" , but after the oil warms up and thins out....Knock,Knock,....
Just an idea, I hope it's not a Crank, but I learned with those AMC engines to just grind em and get it over with ,no matter how good they look. The Fit size is on the back of the bearing shells, but you must put those shells back on the crank pin they came off of !! Can't mix nothin !! Same with Cam lobes, don't be mixing up the lifters, those go back on the same lobe they came off of !! Unless you put in new camshaft and lifters.
If it's a "Ticking" noise, then it's more than likely in the Valve Train.... You might remove a Valve cover and let it idle and listen for the Tick with the cover off, It'll make and oily ,smokey mess, but don't rev it up, just feel each rocker and put a little pressure on em to see if you can determine which is ticking.....Do one side at a time.
A cleaner way is to use a long screw driver and use it as a Stethascope, put the bit against the valve cover and the handle to your ear, move it along the valve cover until you find the lifter or rocker thats making the noise...
Hope this helps, Good luck .... Ohhhhh, Welcome to the Forum ! "BH"