It will be interesting to see what engine people choose when the Bronco goes on sale. My personal choice would be the 2.3 because (of course) it's the one with the manual, and because I've heard good reviews about the 2.3 when it's in the Ranger and Explorer.
I believe it's 2dr vs 4dr that decides the size of the gas tank. Not motor size. You still get the small tank with a 2.7 in a 2 door.advantages and disadvantages to both:
2.3 >> Metal oil pan with direct injection only .. less HP with smaller gas tank
2.7 >> Plastic oil pan with Dual injection (direct and port) ... more HP with bigger gas tank