Does a kit of the HEMTT M984A4 or the M984E1 exist?

Unfortunately, no.  There is a really nice M983 HEMTT Tractor from Trumpeter that just recently came out though. 

You could take it, or the older Italeri M977 HEMMT Cargo (not recommended as it is pretty poorly detailed), and add the Hobby Fan M984A1 resin conversion kit to it.

 

That would get you an M984A1 version, which is a little older. 

M984A1

Like you said, the current version is an M984A4, which has quite a bit of differences. The most prominent differences are a totally redesigned cab, new engine compartment, new large radiators behind the cab, and where/how the spare tire attaches.  All these things would have to be scratch-built, which would require a lot of work.

M984A4

No clue about the E1 version.  To me, it looks no different than the M984A1 version. 

M984E1

I recommend building him the M984A1 and it would be close enough.  I'm sure he would be happy just to have a model of the basic type of vehicle he drove.

The M984E1 was the initial prototype which just became the M984A1 when it was in full production. There was no difference between vehicles other than when they were produced. I think, I am not positive, that the M984 had a small cargo bed instead of the tool compartments found on the M984E1/A1.

Gino and Rob, you guys are AWESOME!  Thanks for the insight and the info.  As someone who is a big dummy when it comes to armor stuff, I find learning new stuff like this to be fascinating.  I appreciate the information and the great pictures.  Thanks again!

Eric

Rob is correct on the original M984 as well.  Here it is with a shortened cargo bed and wrecker gear on back.