Dear Brian:
I can relate to you my friend. First off I tried for years to find something out. Mind you in the beginning it was pretty much an occasional search on the internet (several years back) and I could find NOTHING then. So I pretty much put that aside and thought, oh well. Sigh! But I had tried contacting NARA and the first time I waited months and got no response. I was bummed. I tried again and this time they said I would have to fill out the paper work again for some reason. Well I did that and still nothing. More sighing.
When I moved up north in Michigan from Detroit, I thought well, one last try. I DID get a response, but it wasn't what I was expecting. They told me his paperwork had burned in a fire. You can imagine how heartbroken I was. I was in tears. After all this time and then this. 
Well a few months after that, I thought, I am not giving up and started searching Internet again. At first it was almost fruitless, but I kept at it and pretty soon I had a couple of names and some info. It kept me going. Then one day I received a hand-written letter from one of the guys I wrote to. It was about a month after I had mailed it to him. It was from a guy in my dad's unit. They didn't serve in the same company, but he was a member of the 540th. Oh man I was dancing.
Things started coming together slowly after that, but it was really happening. My head is still spinning. 
Well onto the Army Corps of Engineers. They were my main source of information. I contacted the head historian there and within a couple of weeks, he called me on the phone. I was so impressed. Said they were sending me a big envelope with all kinds of documents. I was just thrilled.
So please DO contact them. They have folders on virtually every unit. Some are more comprehensive than others. The 540th were "popular", so I was lucky. Other units may just have a few sheets of documentation, but it's worthwhile my friend. 
If you go to my RESEARCH section here, you will find out more. Included there are all the contact numbers for The Army Corps History Office too. Let me know what you find out. I am more than happy to help.
http://www.6thcorpscombatengineers.com/eng...hp?showtopic=23
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"