Hello Wolfman!
Nice! Just watch out - the Whale is a science for itself with all its variants converted from one to another and back, it's easy to confuse things and I know trumpeter did cofuse things in their 1/48 whales. Unfortunately I can't be too speceific here, because I work in 1/72 and even managed to do this:
More details here:
http://vietnam.net.pl/EKA3Ben.htm
I hope mmy writing helps you. Tommy Thomason also has a lot of good info on the Whale and its models:
http://tailspintopics.blogspot.com/2010/09/mighty-skywarrior.html
There are also other articles there, worth a read if you didn't already.
And please note, if I'm not mistaken (and it's complicated!) - ERA-3B didn't fight in Vietnam - it was a photo recon aircraft (RA-3B) converted to "electronic agressor" for range exercises. This variant belongs to the so-called "Versions" of the Whale, with thick crew doors, reinforced main wheel brakes and with no bomb bay (crew cabin and fuel are in that place). Called this way because it was a special purpose aircraft from the very beginning.
The one fighting in Vietnam was the EKA-3B like in my picture above - this belonged to the so called "bomber" whales - meaning it started its life as a bomber (A-3B), later converted to tanker (KA-3B) later upgraded with ECM gear (EKA-3B). Those aircraft had "thin" crew door, slim main wheel brakes and a large bomb bay.
The Whale was also built in two series - first with normal wing, and the next series with the so-called CLE wing - you can tell them apart by looking at the leading edge of the wing inboard of the engines. If there are slats there, it's a CLE aircraft. If not - it's the initial wing.
See? I told you it's complicated. I'd suggest you ask the CPO about some details (might also be he doesn't care) so that he can have the feeling it's HIS aircraft and not just close!
Good luck with your build - I'll be watching - and have a nice day
Paweł