To post pics here you will need to have them hosted. I've used
Image Shack before. Also seen tinypic.com. There both free. Just need to upload the images and note the url. Place the link between the 2 sets of brackets. Be sure to re-size them before uploading. 640x480 is usually plenty big enough, but if you need to show a hi-res image use the thumbnail option.
For screws I've used 1 5/8" or 2" drywall screw spaced every 3", but you need to find a course thread type, predrill carefully, fully clearance drill the top.
I used similar foam gasket, but I use a careful tightening method. Get them just snug at first all around, then go over each screw again, working from one side to the other. It helps to have someone stand on the top, too, as you snug them up. By the time I get all done the foam is flat. If it's not flat it could leak everywhere there is pressure.
I doubt if that small differential between your baffles will cause any serious problems. I'm sure the psychological stress is far greater than any acoustic effect. Not having the foam compressed would be much more troublesome. The sealed volume needs to match a driver's needs to have a well controlled sound, not too critical, but close is better.
As far as delay, one of the members has a time corrective crossover and had a total delay equal to about 5 meters distance. I can't remember the thread, but if you search the WO forum for group delay you might get lucky.
Welcome!