Engine noise reduction and power increase?

Hello everyone.

Tomorrow I'm planning on buying a 1986 LT35
motorhome with 6cyl turbodiesel (intercooler) engine. So far, my only
experience with LTs has been a test drive of an LT28 a few days ago. One
of the things which struck me about it was how the engine noise was
really penetrating into the cockpit. I also noticed how I couldn't comfortably build a speed above 80km/h. Are these things to be expected with all LTs or did I possibly test drive a banger?  I'm really keen on the one I'm going to look at tomorrow but some advice could really go a long way towards helping me make this big decision. If I find that the noise level is actually normal, are there any known means to reduce this without using bitumen based sound deadener. I was thinking that since the engine is located in the space between the two front seats could I just place a localised sound proofing box over this (a bit like the noise reducing boxes they use for generators)? Has anyone had any luck placing materials over this space and actually making any difference? I was even thinking about some custom made and carefully position sand bags covered with acoustic blanket and carpet. Knowing that something can be done will really help me make that decision as everything else about the van is perfect.
Also, Other than a full engine replacement, are there any modifications which can be done to increase max cruising speed? I do like this van, so I could spend a few K replacing the engine if I have to. If that is recommended, would anyone have any suggestions, bearing in mind that I'm planning on installing a vegetable oil kit so that I can run it on pure veggie oil.
Many many thanks!
Pete

I would imagine that a turbo is the best sound deadener. And as a turbo engine is working more relaxed it want make that much noice, so i think it will be much more comfortable. Look from 4min into this video https://www.youtube.com/watch?v=_enTrQKgOrQ I think he has a TD-IC engine. It sounds a lot more silent than mine with the mighty 75hp engine.
Is it aproved with the TD-IC engien in it? Mine has 75hp in the registration papers, so for me it is a problem to instal something bigger and get it aproved. And the importer, Scumbag-Møller say they don't have anny information on the VW LT1 at all. So i can't even instal a 102hp turbo engine.
It is not rocket science to instal a 5syl 2,5TDI engine in it. A guy in Austria has instaald a 140hp 2,5TDI and chiped it to 180hp.
In my 87 Karmann LT L i've decided to live with the noice. On my GPS it does 108km/h max but we cruise at 85-90kmh (GPS) on flat rooads. Up the Lierbakken hill we do about 65kmh With the weight of 3100kg

The chap who made the film is Tim Aldiss and he's a member of VOLT, you can join the Facebook group here: 
http://www.facebook.com/groups/voltowners/?multi_permalinks=10156446837549421&notif_id=1524987616438101&notif_t=group_activity&ref=notif