Congratulations on your Mossberg 500A! Did it come with any spare chokes and if not do you know which one is installed on the barrel? I only ask because if you plan to shoot some slugs out of it you want nothing tighter than a modified but I personally suggest nothing tight than an improved cylinder. I know my Mossberg 500 will only fit 5 no matter what rounds I put in it. There is a tab bit of extra room but certainly not enough to get another shell in. Its great that you were able to track down the build date of your Mossberg 500A. Most Mossberg 500 will have jiggle to the front pump but it shouldn't be "loose". The loose tolerances are part of what make the Mossberg 500 such a reliable firearm. The safety should be smooth so you may have to strip down the receiver and lube everything up and make sure there is no rust or debris causing it to be stiff.