I do not think you NEED wheel weights in your application if your rear tires are loaded. As has been mentioned, wheel weights and/or hitch mounted ballast really do help with loader safety and performance. JD specifies a lot of weights, and probably would advise you to have both more wheel mounted weight and either a heavy ballast box or hitch mounted implement for ballast too. I successfully and (mostly) safely used a 300 cx loader on a 3720 tractor which had loaded R4 tires without additional ballast at times. I always tried to run my rear BB (about 500 pounds) when using the loader but there were tight areas on my property that prohibited this some of the time. On flattish ground the 3720 was fine whenever I did this; only once when positioning a big landscaping rock did I encounter wheel lift and instability, but I never felt in imminent danger. By comparison, your 4105 is a larger machine than a 3720 (though it does not weigh more) so unless you are testing your machine's lift capacity on uneven ground you should be fine in most cases. Please bear in mind that I stated you "should be fine" not that you "would be fine" and clearly more weight would be both safer and increase your productivity substantially.
John M