hard clunk in reverse??

Welcome aboard, you've come to the right place for A-bodies. :) Regarding the tranny not going into reverse when it's cold, those tranny's won't fill the torque converted with the selector in Park, so you should always run it in Neutral for a little while to get the fluid circulating and warmed up. Also ensure your fluid level is correct, and it probably wouldn't hurt to have the fluid and tranny filter replaced if both are old and especially if the fluid smells burnt at all. As far as the clunk is concerned, I doubt it is comming from the tranny. First, check your u-joints, front and rear, to make sure the problem isn't there. Next, check rear end for play by putting the rear in the air and, with the trans in park, move one of the wheels forward then backward with a little authority to see if the noise can be isolated. Hope this helps.