Only my 2pence worth so don't shoot me!
I fully understand that it would be best done in a unit.What if The main (mechanical if wanted)parts were done prior but from the outside it still looked ordinary.Is there no way this could then be completed at a weekend meet in the great outdoors.I know for sure if i was at any meet and i came across a large group nutters banging/welding/swearing/building something outside i would be f%%kin hypnotised and would HAVE to stand and watch it being done.Also im sure if the site members even the no talkers knew this was gonna happen then i reckon it would be your biggest most memorable meet ever.You could try to do it at a multi van meet and show them other vanners not to mess with the "ford transit 45th"
Make the van look a nail (if you have nice replacement bumpers make sure the ones on arrival are rusty and twisted.Same with sld dirrty twisted rust replaced with nice windowed one but have it planned to perfection.If you know the van model some gifted chippie type with same model does a mock up interior at home as he has same model same dimensions then brings on the day and fits.This way could easily be done in a weekend and helps the "health and safety crew".
"Keep spanner storming" Its a good topic but would make a much better reality

1More thing tinker with the idea ("WEEKENDER IN A WEEKEND" "TRANSFORUM A STATE IN 48")then maybe contact these
http://www.guinnessworldrecords.com/mem ... eaker.aspx