The 2SE is a progressive 2bbl, 1/2 of a Quadrajet 4bbl, it has a primary and secondary barrel. The 2G is a straight 2bbl, it runs on both barrels all the time. The 2G also has a different bolt pattern requiring an adapter to bolt in place of the 2SE. You would probably lose some mpg with the 2G, and it would require tuning for you 250.
All carbs require maintenance with age. Depending on where it is leaking it may just be a matter of buying a carb kit and cleaning, adjusting the carb. If the leakage is around the throttle shafts then it needs a rebuild. I'd check with your friendly local auto parts store (FLAPS). I just checked NAPA and their showing it's available $559 - Ouch. NAPA also shows 2 dz different carb numbers that their rebuild replaces, that's not good. If that is the original carb, considering age, that's in doubt. I'd keep the old carb core is only $12. The rebuild is probably generic and the old carb (if original) would help tune the rebuild.
Another alternative would be to contact Stovebolt Engineering they sell a Holly/Weber kit that is a progrssive 2 bbl. Their kit is a very poplar kit for the early 235/230/250. The kit would not bolt to your integral head as it is meant as a replacement for a 1bbl, and the bolt pattern on the carbs is also different. Call Tom Langdon at Stovebolt or Patricks they may have another alternative you should be able to find their links on the left column.
Larry
