Bobbe,
Yes, most LNBs are 40mm.
The 36x22 dish you have pointed at 83, you should have no problem adding an LNB at 89 on that dish. As I mentioned, your 36x22 is not much different than my 75e (35 3/4 x 26 1/2) so I would also try adding 72 on that dish (the NBC mux is very strong) as it might come in quite well for you. You also might want to use something like
SatStar - Satellite List to check the satellite strength in your area. If 72 doesn't come in well enough, then you might want to try the same combination on the 1m, with 83 again at the centre.
You could also try 97 (which should come in better than you have been getting, but check the above site) on your dish with 91. As always, it could be line of sight issues and/or interference that could be the culprit.
The point with multiple satellites on various dishes, is to try various combinations until you get some that work. Some satellites are stronger than others, and those are candidates for the off-centre LNBs. Sometimes, due to line of sight issues and interference, or limited space for dishes, you may get it on one dish, whereas a dish just a few feet away, you get nothing (I certainly have had those issues myself!).
I am wondering whether you are getting some interference (on some satellites) from the 4ft dish over top of the 1m dish (after looking at your photo) as the arm and LNB of the 4ft look to be in the line of sight of where the signals would be if pointed in a similar direction. What satellite is the 4ft pointed at?