Check the lever spring, if it has tension on it you will not be able to but the bolt thru. You can relieve the tension on this by loosening the screw on the bottom of the receiver, or by prying up on the spring with a screwdriver.
The lever spring will not let you get the bolt started if you do not loosen it also loosen the screw for the spring on the other side that puts tension on the lifter. The main spring should not affect you trying to put the lower tang back into place. When you put it in just START the screws on either side of the receiver then the lever screw should slide into place. Sometimes they are quite tight when the gun is new. Try cleaning the surfaces on the lower tang that mate with the receiver and then put a little white lithium grease on it. It should be a little easier to assemble. wM1
Sometimes things will be a little skewed on the fit of the lower tang. I have one that is difficult to line up and difficult to remove the lower tang. Its almost as if the frame is a tad off also the lever screw will back out by itself and has to be retightened. However it is my best running rifle. wM1
How the dickens did you get it off without removing the stock in the first place? I guess I shoulda asked but I just figured you would automatically remove the stock to take the lower tang off. I just stripped and cleaned 3 of them today (2 '73's and a '66). wM1
The tang is held in place by the lever screw and the two screws on either side of the receiver. when you remove the lever screw without taking the stock off the bolt that goes though the top tang and into the bottom tang would put tension on it making it difficult at best to get the lever screw back in. wM1