Can't go wrong either way, both have their finnicks. The new G2 is a little more "user friendly", but the trigger needs some work. The G2 is a bit stronger than the old Contender, so you can get away with a few cartridges that might be too much for the old Contender (ie, 30-40 Krag, 444 Marlin, 7.62x39)
If it were me, I'd go ahead and get a G2. Some of the old barrels may have to be persuaded to fit the G2 frame and function properly, but it's not hard to do. Also, the old Contender frames in good condition will cost you as much as a G2.
You are not "supposed" to convert a pistol into a carbine, or convert a rifle into a pistol. If you do it, don't wave it around because according to the law, you are not "supposed" to do this and could be in big trouble for doing this if you were to draw the attention of the BATFE. I figgure that you'll need to be doing something really stooopid (and have your converted Contender with you at the same time) to get caught, but now you have been warned.