About to design an AWACs based off one of my commercial airliners. My first, primary and only concern is that of what airframe to base it on.

Airframe 1 is roughly comparable to a 737, but slightly larger and more expensive with greater range and slightly greater speed.

Airframe 2 is roughly comparable to a 777, near identical in size but with a slightly greater range and speed.

I was thinking of using airframe 2 because of its huge range advantage over airframe 1, but 2 is also significantly larger than 1 and despite using only 2 engines, it would still consume more fuel.

Im not overly aware of how big an AWACs suite is, or if there is any advantage to carrying a larger one, so can somebody please help me out?

Most AWACS have extra room left after the radar and puters so they have extra fuel aboard.

TBH if building an AWACS today, I'd base it on something of a bit older design. You don't need as much size as A380, and 4 engines is a definite plus.

Another option could be a 4-engined version of 787, but then you'd have to wait for 787 to enter service before you can develop the AWACS itself (and metal airframes are easier to modify)... so it won't be soon. As such, A340 is a reasonable pick. Or a 4-engined 777.