While I would agree on the above for the first prototype of a Diezel amp I generally will stay away from such statements

Peter Diezel started with modding Marshalls in his early career days and first prototype of a genuine Diezel amp was on a Marshall chassis with something like 20 tubes mounted. I've seen a photo somewhere. Looked like The Holly Father of Frankensteined amps
As of VH4 - it is in class of its own. Soundwise, may closely emulate Marshall, but that's it. And is only one of the gazillion possibilities there. Heavy rhythm and lead tones there are nowhere near Marshall. Lead channel (was 4 if I remember correctly) is insanely liquid, fat and in the same time cut-through-the-mix tone that it's unbelievable until heard.
An over-engineered beast with exceptional attention to the detail and especially the tone.
So, if you are not Peter Diezel, I do not think that you'll be getting to anything modding a Marshall to sound like Diezel. Certainly, there are Marshall mods available around, that will certainly change the way the amp sounds, in a hopefully positive way, but if you want a Diezel sound - save some cash and get the amp.