The poor quality Magneteks mentioned previously are the 6300 series, which is notorious for ruining batteries by overcharging till they run dry, yet slow to recharge under normal conditions. I don't know if the 700 series shares that defect or not. If you are not having problems with the water boiling off the batteries when left on charge for a few weeks at a time, you may be ok with what you have. If, however, your battery life is short, or the converter is objectionably noisy (loud hum), you should consider replacing it.
The Xantrex you cited is one of several excellent converter/chargers. Some others are Iota and Progressive Dynamics. Parallax Power, which is the new name for Magnetek, recommends the Parallax Power 7400 series as the replacement, but it's only a two stage charger whereas the others are three (superior).
The Magnetek 740 is a 40A charger of the ferro-resonant type. It should be easily replaceable with the Xantrex if there is physically room for it - I think the Xantrex is a slightly different shape. It was later replaced with the 900 series (e.g. 940) and that was a decent converter/charger. Can't find any good info on the 740, though. Here is the Parallax Power page that has a bit of info on their obsolete chargers:http://www.parallaxpower.com/ferro.htm
The Xantrex will have two large wires that go to the battery terminals or to an electrical bus terminal that leads right to the battery) plus a 3 wire 120vac power cord connection (a standard 120vac power plug is optional on that model). If your current converter hooks up the same way, its a snap.