Also 4wd would be another option I would recommend. My kubota didn't come with the sliding tube stabilizers, just the turn buckle type, but I think it can be a dealer add on.
My advise if he is looking for a tractor to keep from now own is go for the most comfortable model of the 3 you mentioned. I would lean more toward the L models for the heavier frame strength but it will bug him from now own if he gets one and really wanted one of the others. With all of them being so close in size there won't be a huge difference in power.
B 3300 hst only; 33hp-25pto/9.9 hyd/3pt 1400/live pto/1764#
L 2800 gear; 28.6hp-25pto/10.5 hyd/3pt 1435/over run pto/2536#
L 3400 gear; 34.2hp-30pto/10.1 hyd/3pt 1435/live pto/2580#
Not a big difference between any of them but look at the 3pt lift cap. and then look at the weight of the tractors. Which one would you feel safer picking up the rated capacity?
I would make 4x4 a must. 30 -35hp 4x4 is equal to 45 - 50hp 2wd as far as pushing power goes and will also be a big plus using a fel.
I have a L 3000 DT 32hp and it handles my 62" tiller with no problem so I would think any of the models he is interested in will handle a 60" just fine.
As far as the stabilizers go those models (as far as I know) come with the turn buckle style on them. With all the new models that have the telescoping type on them now this will probably apply to them but I know for sure that the stabilizers off of a L 4300 is a direct replacement for the turnbuckles. That is what I ordered for mine and they are definately worth every penny spent to change them out.
I think the best choice out of the 3 would be the L 3400. Heaviest tractor of the 3, live pto and biggest ci engine.
Right now is a great time to buy a new Kubota due to the 0% financing for 60 months. Now thru 5-31-2010.